Sunscreen use: controversies, challenges and regulatory aspects

Evaluation of In Vitro Metabolism- and Transporter-Based Drug Interactions with Sunscreen Active Ingredients

PURPOSE

The aim of this study was to examine the ability of sunscreen active ingredients to inhibit in vitro drug metabolism via cytochrome P450 (CYP) enzymes and drug uptake transporters.

METHODS

Metabolism assays with human liver microsomes were conducted for CYP2C9, CYP2D6 and CYP3A4 using probe substrates warfarin, bufuralol and midazolam, respectively. Uptake transporter assays with transfected cell lines were conducted for OAT3, OCT2 and OATP1B1 with probe substrates estrone-3-sulfate, metformin and rosuvastatin, respectively. Six sunscreen active ingredients, avobenzone, enzacamene, oxybenzone, octinoxate, trolamine, and homosalate, were evaluated up to their aqueous solubility limits in the assays.

RESULTS

None of the sunscreen active ingredients inhibited CYP2D6 or CYP3A4 activities in the microsomes at concentration ranges up to tenfold higher than their known clinical total plasma levels. Only enzacamene, oxybenzone and trolamine were found to be inhibitory to CYP2C9 activity with IC50 values of 14.76, 22.46 and 154.7 µM, respectively. Avobenzone, enzacamene, homosalate and octinoxate were not inhibitory to the uptake transporters at the evaluated concentrations. Oxybenzone was inhibitory to OAT3 and OCT2 with IC50 values of 39.93 and 42.77 µM, respectively. Trolamine also inhibited uptake in OAT3 and OCT2 transfected cells with IC50 values of 448.1 and 1376 μM, respectively.

CONCLUSIONS

Although enzacamene, oxybenzone and trolamine inhibited CYP2C9 and the renal transporters OAT3 and OCT2 in vitro, their IC50 values exceeded total plasma levels found in clinical studies. Therefore, it is unlikely that these sunscreen active ingredients in sunscreen products will inhibit the metabolism or transport of co-administered drugs in consumers.

Photoprotective efficacy of Sunset Yellow via inhibition of type-I and type-II pathway under exposure of sunlight

Exposure to phototoxicants and photosensitizers can result in the generation of reactive oxygen species (ROS), leading to oxidative stress, DNA damage, and various skin-related issues such as aging, allergies, and cancer. While several photo-protectants offer defense against ultraviolet radiation (UV-R), their effectiveness is often limited by photo-instability. Sunset Yellow (SY), an FDA-approved food dye, possesses significant UV-R and visible light absorption properties. However, its photoprotective potential has remained unexplored. Our investigation reveals that SY exhibits remarkable photostability for up to 8 h under both UV-R and sunlight. Notably, SY demonstrates the ability to quench ROS, including singlet oxygen (1O2), superoxide radicals (O 2 · - $$ {\mathrm{O}}_2^{\cdotp -} $$ ), and hydroxyl radicals (·OH) induced by rose bengal, riboflavin and levofloxacin, respectively. Moreover, SY proves effective in protecting against the apoptotic and necrotic cell death induced by the phototoxicant chlorpromazine (CPZ) in HaCaT cells. Further, it was observed that SY imparts photoprotection by inhibiting intracellular ROS generation and calcium release. Genotoxicity evaluation provides additional evidence supporting SY's photoprotective effects against CPZ-induced DNA damage. In conclusion, these findings underscore the potential of SY as a promising photoprotective agent against the toxic hazards induced by phototoxicants, suggesting its prospective application in the formulation of broad-spectrum sunscreens.

Redefine photoprotection: Sun protection beyond sunburn

Excessive exposure to ultraviolet (UV) light leads to acute and chronic UV damage and is the main risk factor for the development of skin cancer. In most countries with western lifestyle, the topical application of sunscreens on UV-exposed skin areas is by far the most frequently used preventive measure against sunburn. Further than preventing sunburns, increasing numbers of consumers are appreciating sunscreens with a medium- to high-level sun protective factor (SPF) as basis for sustainable-skin ageing or skin cancer prevention programs. However, recent investigations indicate that clinically significant DNA damages as well as a lasting impairment of cutaneous immunosurveillance already occur far below the standard of one minimal erythema dose (MED) sunburn level, which contributes to the current discussion of the clinical value of high-protective SPF values. Ex vivo investigations on human skin showed that the application of SPF30 reduces DNA damage for a day long sun exposure (24 MED) drastically by about 53% but is significantly surpassed by SPF100 reducing DNA damage by approx. 73%. Further analysis on different SPF protection levels in UV-exposed cell culture assays focusing on IL-18, cell vitality and cis/trans-urocanic acid support these findings. Whereas SPF30 and SPF50+ sunscreens already offer a solid UVB cover for most indications, our results indicate that SPF100 provides significant additional protection against mutagenic (non-apoptotic-) DNA damage and functional impairment of the cutaneous immunosurveillance and therefore qualifies as an optimized sunscreen for specifically vulnerable patient groups such as immunosuppressed patients, or skin cancer patients.

When should sunscreen be applied: The balance between health benefit and adverse consequences to humans and the environment

OBJECTIVE

To propose a strategy for using sunscreens that optimizes the balance between skin health and adverse effects to humans and the environment.

METHODS

A model was developed to explore the relationship between sunscreen usage and personal sun exposure throughout the year in populations resident at different latitudes.

RESULTS

There is little biological justification in terms of skin health for applying sunscreen over the 4-6 winter months at latitudes of 45° N and higher, whereas year-round sunscreen is advised at latitudes of 30° N and lower. Avoiding sunscreen application at times when it is biologically unnecessary results in an annual reduction in sunscreen use of 25%. Furthermore, using products containing UV filters over the winter months at more northerly latitudes could lead to a higher number of people with vitamin D deficiency. The single largest use of sunscreen is on a sun-seeking holiday and encouragement to make more use of clothing and shade would appreciably reduce the sunscreen burden to the environment.

CONCLUSION

We need to use sunscreens wisely so that we gain the health benefit from their use while at the same time limiting possible harm to ourselves and the environment.

Will warmer summers increase the impact of UV filters on marine bivalves?

Marine organisms are constantly exposed to multiple stressors including pollutants released into the environment, such as personal care products (PCPs), and climate change-derived factors, namely warming, which are aggravated by anthropogenic drivers and pose increasing pressure on coastal ecosystems. Avobenzone (AVO) is one of the most used ultraviolet (UV) filters in PCPs which have been increasingly used and, thereby, identified in aquatic environments. However, data regarding the influence of warming on the impacts caused by AVO in bivalves is lacking. Mussels are considered good bioindicators thus being often employed in ecotoxicology studies. Hence, the present study aimed to evaluate the toxic effects of an environmentally relevant concentration of AVO (0.5 μg/L) and warming (21 °C), acting alone or in combination, on sperm and adults of the Mediterranean mussel species Mytilus galloprovincialis, through in vitro and in vivo tests, respectively. AVO and warming effects were evaluated by assessing oxidative status, viability, genotoxicity, motility, and kinetics in sperm, together with the quantification of energy content, metabolic capacity, biological defence mechanisms, cellular damage, and neurotoxicity in adults. AVO induced genotoxicity and increased respiration rate in sperm while enhancing the biotransformation enzymes' activity in adults. Exposure to warming led to an increase in respiration rate, ROS overproduction, cellular damage, and viability decrease in sperm whereas metabolic capacity increased in adults. AVO combined with warming caused oxidative stress, cellular damage, genotoxicity, and decreased motility in sperm, while only antioxidant enzymes' activity was enhanced in adults. Overall, the present study demonstrated that when acting in combination the effects of both stressors were more prominent. Furthermore, considering the multiple-stressor scenario tested, major toxic effects occurred in male gametes in comparison to adults.

Determining the ability to differentiate results between independent sun protection factor tests using the ISO24444 method

Introduction

The sun protection factor has nowadays become a familiar metric to understand sunscreen effectiveness. This value is displayed on the label of sunscreens and it is established by translating the results obtained from standardized testing methods to regulatory labeling criteria. The ISO24444, a widely accepted method to measure the sun protection factor, is designed to determine the validity of a single test, but it lacks criteria to compare results and many regulators only endorse the method as a valid means to label sunscreens. This supposes a challenge for manufacturers and regulators routinely using the method to take decisions on product labeling when confronted with disparate results for the same product.

Methods

Analytical review of the statistical criteria used by the method to determine test validity.

Results

For the same product, results from independent tests (of 10 subjects each) separated less than ×1.73 can be considered as the same from the point of view of compliance to the standard.

Conclusion

This range of sun protection factor values far exceeds the ranges for labeling and categorizing sunscreens as per current regulations and thus opens the possibility that sunscreens are unknowingly mislabeled. These findings can be summarized in a "discriminability map" to assist comparing results from different tests and to better inform the labeling of sunscreen products and thus increase confidence to prescribers and consumers.

In vitro spermiotoxicity and in vivo adults' biochemical pattern after exposure of the Mediterranean mussel to the sunscreen avobenzone

Avobenzone (AVO) is one of the most frequent ultraviolet (UV) filters in personal care products (PCPs). The Mediterranean mussel Mytilus galloprovincialis is a bioindicator often used for ecotoxicological research. Since UV filters reach higher peaks during summer in aquatic bodies, coincident with mussels' spawning period, and bivalves are sessile, both male gametes and adults of this species were used in this experiment. Therefore, the present study aimed to assess how AVO affects M. galloprovincialis at different biological levels. In vitro experiments on sperms (30 min-exposure) and in vivo experiments on adults (28 days-exposure) were carried out at 0.1, 1.0 and 10.0 μg/L of AVO concentrations. The oxidative and physiological status together with genotoxicity in exposed sperms were assessed. Several biochemical parameters related to enzymatic antioxidant defences, biotransformation enzymes, cell membrane damage, energy reserves, and neurotoxicity were evaluated in adult mussels. Results of in vitro sperm exposure to AVO showed significant overproduction of superoxide anions and DNA damages in all treatments and decrease in sperm viability at 1.0 and 10.0 μg/L. AVO exposure also led to complete inhibition of motility of sperms at the highest concentration, while a significant increase of curvilinear velocity and decrease of wobble occurred at 1.0 μg/L. In vivo exposed adults exhibited a significant decrease in metabolic capacity at 0.1 μg/L, a significant increase in the total protein content and enzymatic turnover as superoxide dismutase (antioxidant defence) at 10 μg/L. This study revealed an ecological concern related to the high sensitivity of sperms respectively to adults under environmentally relevant concentrations of AVO, underpinning an hypothesis of male reproductive function impairments.

Salicin and Hederacoside C-Based Extracts and UV-Absorbers Co-Loaded into Bioactive Lipid Nanocarriers with Promoted Skin Antiaging and Hydrating Efficacy

Conventional and herbal active principles can be combined in a beneficial harmony using their best features and compensating for the certain weaknesses of each. The study will answer the question, “how can willow bark extract (Wbe) or ivy leaf extract (Ile) influence the photoprotective, skin permeation and hydration properties of Bioactive Lipid Nanocarriers (BLN) loaded with UV-filters and selected herbals?”. BLN-Wbe/Ile-UV-filters were characterized for particle size, zeta potential, thermal behavior, entrapment efficiency and drug loading. The formulated BLN-hydrogels (HG) were subjected to in vitro release and permeation experiments. The in vitro determination of sun protection factors, as well as comparative in vitro photostability tests, rheology behavior and in vivo hydration status have been also considered for hydrogels containing BLN-Ile/Wbe-UV-filters. Photoprotection of BLN-HG against UVA rays was more pronounced as compared with the UVB (UVA-PF reached values of 30, while the maximum SPF value was 13). The in vitro irradiation study demonstrated the photostability of BLN-HG under UV exposure. A noteworthy cosmetic efficacy was detected by in vivo skin test (hydration effect reached 97% for the BLN-Wbe-UV-filters prepared with pomegranate oil). The research novelty, represented by the first-time co-optation of the active herbal extracts (Wbe and Ile) together with two synthetic filters in the same nanostructured delivery system, will provide appropriate scientific support for the cosmetic industry to design novel marketed formulations with improved quality and health benefices.

Degradation of 2-phenylbenzimidazole 5-sulfonic acid by UV/chlorine advanced oxidation technology: Kinetic model, degradation byproducts and reaction pathways

In this study, the degradation kinetic model and pathways of a UV filter, 2-phenylbenzimidazole-5-sulfonic acid (PBSA) during UV/chlorination were investigated. PBSA hardly degraded under UV irradiation or chlorination alone, but its degradation in UV/chlorination was efficient and followed pseudo-first order kinetics at pH 7. Increasing the chlorine dosage from 12.5 to 200 μM can enhance PBSA degradation, while increasing pH from 5 to 9 caused opposite effect. The second-order rate constants between radicals (∙Cl, ∙ClO, and ∙OH) and PBSA and the contribution of ∙OH during UV/chlorination were determined. ∙Cl and ∙OH were confirmed to be the main contributors to PBSA degradation. The presence of background [Formula: see text] and humic acid can inhibit PBSA degradation, but the presence of Cl^- showed negligible effect. Kinetic model was established, and the prediction correlated well to the experimental results. The mineralization rate in terms of total organic carbon increased with reaction time to 44.9% after 60 min UV/chlorination. The PBSA degradation intermediates in UV/chlorination were identified, and the transformation pathways were proposed accordingly. Furthermore, the formation of chlorinated disinfection by-products (Cl-DBPs) were evaluated in the sequential chlorination for comprehensively evaluation of the efficiency, mechanism, and safety of removing PBSA using UV/chlorination.

Stimulating Sunscreen Use Among Outdoor Construction Workers: A Pilot Study

Background

Outdoor workers (OW) receive a higher dose of ultraviolet radiation (UVR) compared to indoor workers (IW) which increases the risk of non-melanoma skin cancer (NMSC). Regular sunscreen use reduces the NMSC risk, however, adequate sun-safety behavior among OW is poor. The main objective was to conduct method- and intervention-related elements of a future intervention trial among OW, based on providing sunscreen and assessing sunscreen use on group- and individual level.

Methods

This pilot study was conducted at a construction site in the Netherlands from May-August 2021. Nine dispensers with sunscreen (SPF 50+) were installed at the worksite. OW (n = 67) were invited to complete two (cross-sectional) questionnaires on sun-safety behavior, before and after providing sunscreen. Stratum corneum (SC) samples for the assessment of UV-biomarkers were collected from the forehead and behind the ear from 15 OW and 15 IW. The feasibility of the following elements was investigated: recruitment, (loss to) follow-up, outcome measures, data collection, and acceptability of the intervention.

Results

The first questionnaire was completed by 27 OW, the second by 17 OW. More than 75 percent of the OW were aware of the risks of sun exposure, and 63% (n = 17) found sunscreen use during worktime important. The proportion of OW never applying sunscreen in the past month was 44.4% (n = 12) before, and 35.3% (n = 6) after providing sunscreen. A majority of OW (59.3%, n = 16) found sunscreen provision encouraging for sunscreen use, the dispensers easy to use (64.7%, n = 17) and placed in practical spots (58.8%, n = 18). Collecting SC-samples was fast and easy, and several UV-biomarkers showed higher levels for sun-exposed compared to less exposed body parts. There was no significant difference in UV-biomarker levels between OW and IW.

Conclusions

This pilot study revealed low sunscreen use among OW despite providing sunscreen, overall satisfaction with the sunscreen, and the sufficient awareness of the risks of UVR-exposure. Collecting SC-samples at the workplace is feasible and several UV-biomarkers showed to be promising in assessing UVR-exposure. The low participation rate and high loss to follow-up poses a challenge for future intervention studies.

Applications and Biocompatibility of Mesoporous Silica Nanocarriers in the Field of Medicine

Mesoporous silica nanocarrier (MSN) preparations have a wide range of medical applications. Studying the biocompatibility of MSN is an important part of clinical transformation. Scientists have developed different types of mesoporous silica nanocarriers (MSNs) for different applications to realize the great potential of MSNs in the field of biomedicine, especially in tumor treatment. MSNs have achieved good results in diagnostic bioimaging, tissue engineering, cancer treatment, vaccine development, biomaterial application and diagnostics. MSNs can improve the therapeutic efficiency of drugs, introduce new drug delivery strategies, and provide advantages that traditional drugs lack. It is necessary not only to innovate MSNs but also to comprehensively understand their biological distribution. In this review, we summarize the various medical uses of MSN preparations and explore the factors that affect their distribution and biocompatibility in the body based on metabolism. Designing more reasonable therapeutic nanomedicine is an important task for the further development of the potential clinical applications of MSNs.

Global trends of sunscreen research literature: A bibliometric analysis over the period of 2010–2020

Objective:

Materials and Methods:

Results:

Conclusion:

Stratum corneum biomarkers after in vivo repeated exposure to sub-erythemal dosages of ultraviolet radiation in unprotected and sunscreen (SPF 50+) protected skin

BACKGROUND

There is a need for non-invasive biomarkers to assess in vivo efficacy of protective measures aiming at reducing ultraviolet radiation (UVR) exposure. Stratum corneum (SC) biomarkers showed to be promising markers for internal UVR dose and immune response.

PURPOSE

To establish a dose-response relationship for SC biomarkers and explore their suitability for in vivo assessment of the blocking effect of two sunscreens with a high sun protection factor (SPF) (50+).

METHODS

Twelve volunteers were exposed to a broad-spectrum UVB (280-320 nm), five times a week, during one week. Unprotected back skin was irradiated with 0.24, 0.48, 0.72 and 1.44 standard erythema dose (SED) and sunscreen-protected skin with 3.6 SED. SC samples for determination of the relative amount of cis-urocanic acid (cUCA) and thirteen immunological makers including cytokines and matrix metalloproteinases (MMP) were collected after each irradiation.

RESULTS

cUCA sharply increased after the first irradiation in a dose-dependent fashion. However, it levelled-off after subsequent exposures and reached a plateau for the highest UV-dose after the third irradiation. None of the immunological markers showed dose-dependency. However, MMP-9, IL-1β and CCL27 increased gradually from baseline during repetitive exposures to the highest UV-dose. Assessed from cUCA, both sunscreens blocked >98% of the applied UV-dose.

CONCLUSIONS

cUCA is a sensitive, non-invasive marker of the internal UVR dose enabling in vivo assessment of the blocking effect of high SPF sunscreens in the UVB-region. Immunological SC markers show low sensitivity in detecting immune response at sub-erythemal UVR dosages, suggesting they might be suitable only at higher and/or repetitive UVR exposure.

Elucidating the Photoluminescence Quenching in Ensulizole: an Artificial Water Soluble Sunscreen

Employing natural or artificial sunscreens is essential to protect the skin from ultraviolet radiations that cause premature aging and develop melanoma and other forms of skin cancer. The 2-Phenylbenzimidazole-5-sulfonic acid, commonly known as ensulizole is a water-soluble artificial sunscreen that absorb UV-B (280 nm - 315 nm) radiations and protects the skin against the harmful effects of these radiations. We have measured steady-state photoluminescence (SSPL) spectra and photoluminescence (PL) kinetics of this compound in various conditions. Steady-state absorption indicates a strong absorption feature at 303 nm and a weak one at 316 nm that have been identified as π → π* and n → π* transitions, respectively. The spectra of PL induced by these absorptions indicate that the PL of ensulizole is less Stokes-shifted in polar solvents and more Stokes-shifted in non-polar solvents. The average PL lifetime of ensulizole is longer in non-polar solvents than in polar solvents and it exhibits the shortest PL lifetime in aqueous medium that maximize its transition efficiency in water. This suggests in non-polar solvents intersystem crossing is the dominant mode of relaxation of the excited ππ* state. Furthermore, an increase of pH of ensulizole solution decreases the PL intensity and the lifetime. Stern-Volmer equation is employed to evaluate bimolecular quenching rate constant kq. The evaluation result suggests the diffusional dynamic mode of PL quenching is operative.

Hydrogel sunscreen based on yeast /gelatin demonstrates excellent UV-shielding and skin protection performance

Traditional organic and inorganic sunscreens suffer from the disadvantages of low stability and poor biocompatibility. In the study, we developed a novel hydrogel sunscreen based on the yeast and gelatin, which demonstrated excellent UV protection property and broad absorption of UV across UVA and UVB region. Yeast was used as effective component and gelatin as matrix to fabricate the hydrogel, which is high hydrated and reasonable to simulate natural living tissue. As a common probiotic, yeast shows safety and satisfactory UV protection capability. Furthermore, the hydrogel sunscreen shows excellent biocompatibility and UV protection performance both in vitro and in vivo. Moreover, they can be prepared conveniently and provide an eco-friendly strategy, which provides experience and inspiration of probiotics in the cosmetics application.

Evaluation of drug-likeness and ADME properties of sunscreens and preservatives using reversed-phase thin layer chromatographic retention data and calculated descriptors

RP-18 TLC chromatography was used to evaluate the pharmacokinetic properties (volume of distribution, V_D; plasma protein binding, %PPB; the ability to cross the blood-brain barrier expressed as log PS and log BB) of several cosmetic raw materials - sunscreen and preservatives. The majority of these compounds are intended for topical use on skin and their drug-likeness and the ability to cross biological barriers are undesired. The retention parameters R_M⁰, S, PC₁ and R_M^{75 %} obtained for mobile phases containing six organic modifiers (methanol, acetonitrile, THF, acetone, dioxane, DMF) were used as the sole descriptors or combined with calculated physicochemical properties (PSA, M_W, V_M) of studied compounds. The chromatographic parameters considered in this study are, generally speaking, good predictors of the compounds' pharmacokinetic properties V_D, %PPB and log PS. R_M^{75 %} and the novel parameters derived from it (R_M^{75 %}/M_W and R_M^{75 %}/V_M) can be considered time- and cost-effective alternatives to the chromatographic parameters obtained by extrapolation or interpolation methods. In the case of some pharmacokinetic properties investigated in this study additional descriptors (PSA) have a significant influence on the quality of correlations.

Protection Against Solar Ultraviolet Radiation in Outdoor Construction Workers: Study Protocol for a Non-randomized Controlled Intervention Study

Introduction: Non-melanoma skin cancer (NMSC) incidence is increasing, and occupational solar exposure contributes greatly to the overall lifetime ultraviolet radiation (UVR) dose. This is reflected in an excess risk of NMSC showing up to three-fold increase in outdoor workers. Risk of NMSC can be reduced if appropriate measures to reduce UVR-exposure are taken. Regular use of sunscreens showed reduced risk of NMSC. However, sun-safety behavior in outdoor workers is poor. The objective of this study is to investigate the effectiveness of an intervention aiming at increasing sunscreen use by construction workers.

Methods: This non-randomized controlled intervention study is comprised of two intervention and two control groups recruited at four different construction sites in the Netherlands. The study population comprises ~200 construction workers, aged 18 years or older, followed during 12 weeks. The intervention consists of providing dispensers with sunscreens (SPF 50+) at construction sites and regular feedback on the application achieved by continuous electronic monitoring. All groups will receive basic information on UV-exposure and skin protection. Stratum corneum (SC) samples will be collected for measurement of biomarkers to assess internal UV-dose. External UV-dose will be assessed by personal UV-sensors worn by the workers during work-shifts in both groups. To detect presence of actinic keratosis (AK) or NMSC, a skin check of body parts exposed to the sun will be performed at the end of the study. The effect of the intervention will be assessed from data on self-reported sunscreen use by means of questionnaires collected on baseline and after 12 weeks of intervention (primary outcome). Levels of SC biomarkers of internal UV-dose, external UV-dose, number of sunburn episodes, and prevalence of NMSC including AK will be assessed as secondary outcomes. The electronically monitored sunscreen consumption will be assessed as process outcome.

Discussion: This study is intended to provide evidence of the effectiveness of a technology-driven intervention to increase sunscreen use in outdoor construction workers. Furthermore, it will increase insight in the UV-protective behavior, external and internal UV-exposure, and the prevalence of NMSC, including AK, in construction workers.

Trial Registration: The Netherlands Trial Register (NTR): NL8462 Registered on March 19, 2020.

Visible light. Part II: Photoprotection against visible and ultraviolet light

Cutaneous photobiology studies have focused primarily on the ultraviolet portion of the solar spectrum. Visible light (VL), which comprises 50% of the electromagnetic radiation that reaches the Earth's surface and, as discussed in Part I of this CME, has cutaneous biologic effects, such as pigment darkening and erythema. Photoprotection against VL includes avoiding the sun, seeking shade, and using photoprotective clothing. The organic and inorganic ultraviolet filters used in sunscreens do not protect against VL, only tinted sunscreens do. In the United States, these filters are regulated by the Food and Drug Administration as an over-the-counter drug and are subject to more stringent regulations than in Europe, Asia, and Australia. There are no established guidelines regarding VL photoprotection. Alternative measures to confer VL photoprotection are being explored. These novel methods include topical, oral, and subcutaneous agents. Further development should focus on better protection in the ultraviolet A1 (340-400 nm) and VL ranges while enhancing the cosmesis of the final products.

Sunscreens and their usefulness: have we made any progress in the last two decades?

Sunscreens have now been around for decades to mitigate the Sun's damaging ultraviolet (UV) radiation which, although essential for the existence of life, is a recognized prime carcinogen. Accordingly, have suncreams achieved their intended purposes towards protection against sunburns, skin photo-ageing and the like? Most importantly, however, have they provided the expected protection against skin cancers that current sunscreen products claim to do? In the last two decades, there have been tens, if not hundreds of studies on sunscreens with respect to skin protection against UVB (280‒320 nm)-traditionally sunscreens with rather low sun protection factors (SPF) were intended to protect against this type of radiation-and UVA (320‒400 nm) radiation; a distinction between SPF and UVA protection factor (UVA-PF) is made. Many of the studies of the last two decades have focused on protection against the more skin-penetrating UVA radiation. This non-exhaustive article reviews some of the important facets of what is currently known about sunscreens with regard (i) to the physical UV filters titanium dioxide (TiO₂) and zinc oxide (ZnO) and the mostly photo-unstable chemical UVB/UVA filters (e.g., octinoxate (OMC) and avobenzone (AVO), among others), (ii) to novel chemical sunscreen agents, (iii) to means that minimize the breakdown of chemical filters and improve their stability when exposed to UV sunlight, (iv) to SPF factors, and (v) to a short discussion on non-melanoma skin cancers and melanoma. Importantly, throughout the article we allude to the safety aspects of sunscreens and at the end ask the question: do active ingredients in sunscreen products pose a risk to human health, and what else can be done to enhance protection? Significant loss of skin protection from two well-known commercial suncreams when exposed to simulated UV sunlight. Cream I: titanium dioxide, ethylhexyl triazone, avobenzone, and octinoxate; Cream II: octyl salicylate, oxybenzone, avobenzone, and octinoxate.

Simple, green, ultrasound-assisted preparation of novel core-shell microcapsules from octyl methoxycinnamate and oligomeric proanthocyanidins for UV-stable sunscreen

Without sunscreens, UV rays in sunlight cause skin damage, ranging from dark spots and premature aging to skin cancer. Present sunscreens, however, are readily photodegraded, producing highly reactive radicals that can damage cells. To address this problem, we have now used ultrasound to prepare core-shell microcapsules, which offer improved protection against UV light and improved UV stability. The composite microcapsules have oligomeric proanthocyanidins (OPCs), which are amphiphilic plant-derived secondary metabolites, as the shell and octyl methoxycinnamate (OMC), which is a UVB absorber, as the core. The polyphenolic flavonoid structure of OPCs improves the UV stability of OMC and thus avoids the skin damage caused by OMC photodegradation products. In the microcapsules, π-π stacking interactions between OPCs and OMC molecules enhance the ability of OMC to absorb UV radiation and extend the absorption range from the UVB region (280-320 nm) to include the UVA and UVC regions (200-400 nm). The composite microcapsules were shown to be stable on storage and to be non-irritant to human skin. The ultrasound-assisted preparation of OMC/OPCs composite microcapsules is simple, efficient and green and provides a feasible strategy for the development of novel, more effective, sunscreens.

Insights and controversies on sunscreen safety

Although sunlight provides several benefits, ultraviolet (UV) radiation plays an important role in the development of various skin damages such as erythema, photoaging, and photocarcinogenesis. Despite cells having endogenous defense systems, damaged DNA may not be efficiently repaired at chronic exposure. In this sense, it is necessary to use artificial defense strategies such as sunscreen formulations. UV filters should scatter, reflect, or absorb solar UV radiation in order to prevent direct or indirect DNA lesions. However, the safety of UV filters is a matter of concern due to several controversies reported in literature, such as endocrine alterations, allergies, increased oxidative stress, phototoxic events, among others. Despite these controversies, the way in which sunscreens are tested is essential to ensure safety. Sunscreen regulation includes mandatory test for phototoxicity, but photogenotoxicity testing is not recommended as a part of the standard photosafety testing program. Although available photobiological tests are still the first approach to assess photosafety, they are limited. Some existing tests do not always provide reliable results, mainly due to limitations regarding the nature of the assessed phototoxic effect, cell UV sensitivity, and the irradiation protocols. These aspects bring queries regarding the safety of sunscreen wide use and suggest the demand for the development of robust and efficient in vitro screening tests to overcome the existing limitations. In this way, Saccharomyces cerevisiae has stood out as a promising model to fill the gaps in photobiology and to complete the mandatory tests enabling a more extensive and robust photosafety assessment.

Exploring the Photochemistry of an Ethyl Sinapate Dimer: An Attempt Toward a Better Ultraviolet Filter

The photochemistry and photostability of a potential ultraviolet (UV) radiation filter, dehydrodiethylsinapate, with a broad absorption in the UVA region, is explored utilizing a combination of femtosecond time-resolved spectroscopy and steady-state irradiation studies. The time-resolved measurements show that this UV filter candidate undergoes excited state relaxation after UV absorption on a timescale of ~10 picoseconds, suggesting efficient relaxation. However, steady-state irradiation measurements show degradation under prolonged UV exposure. From a photochemical standpoint, this highlights the importance of considering both the ultrafast and “ultraslow” timescales when designing new potential UV filters.

Impacts of UV Filters in Mytilus galloprovincialis: Preliminary Data on the Acute Effects Induced by Environmentally Relevant Concentrations

Ultraviolet (UV) filters are present in a broad range of personal hygiene products, which may be transported via aquatic environments and domestic wastewaters due to inefficient treating station sewage removal and direct human contact. The aim of the present study was to evaluate the potential effects of a UV filter, in particular benzophenone-3 (BP3) (also known as oxybenzone) on the mussel species Mytilus galloprovincialis. Mussels were exposed to this organic substance for 96 h in environmentally relevant concentrations (10, 100, and 1000 ng/L). After exposure, biomarkers related with the mussels’ metabolism and oxidative stress were evaluated. The results revealed significantly higher activity of electron transport system and energy reserves (glycogen and protein (PROT)) at the intermediate concentration of 100 ng/L, suggesting that at lower concentrations mussels’ metabolism was not activated due to low stress. Conversely, at the highest concentration (1000 ng/L), mussels were no longer able to continue to increase their metabolic activity. Higher metabolic capacity was accompanied by increased PROT content associated with increased enzyme production to activate their antioxidant system. Nevertheless, at the highest concentration, cellular damage occurred as a consequence of ineffective activation of antioxidant and biotransformation enzymes. The results of the present study address uncertainties that are fundamental to the environmental risk assessment and management of these economically important near-shore bivalves and other marine species. Although an acute exposure was performed, alterations observed indicate the negative impacts of BP3 towards marine bivalves, which could be enhanced after longer exposure periods or if mussels are simultaneously exposed to other stressors (e.g., other pollutants or climate change related factors). The present study may thus contribute to the definition of fundamental knowledge for the establishment of appropriate regulatory guidelines and practices that ensure the preservation and sustainability of biological resources, allowing for prediction and mitigation of the impacts from these compounds.

Pinterest Homemade Sunscreens: A Recipe for Sunburn

Social media, specifically Pinterest with more than 175 million users, has changed the way people seek and share health information. Recent consumer interest in natural products has led to an increase of shared recipes for homemade products including sunscreen. Homemade sunscreen products are risky because they are not regulated or tested for efficacy like commercial sunscreens. With rising skin cancer rates, the use of effective broadband sunscreen is critical to reduce incidence of skin cancer. This study used directed content analysis to examine how homemade sunscreens were portrayed on Pinterest. Using the search terms, homemade sunscreen and natural sunscreen, researchers sampled every fifth pin to collect 189 relevant pins. A codebook was developed, pilot tested, and used to code pins. Two researchers coded pins and interrater reliability was established at 90%. Of the 189 pins, the majority of pins (95.2%) positively portrayed the effectiveness of homemade sunscreens and 68.3% recommended recipes for homemade sunscreens that offered insufficient UV radiation protection. Sun Protection Factor (SPF) claims were made in 33.3% of pins with a range of SPF 2 to SPF 50. In this sample of pins, 41.8% of pins had been saved by other users ranging from one to more than 21,000 times. Social media is a powerful source of health information. However, this study revealed widespread interest and acceptance of insufficient sun protection information. Pinterest and the interest in homemade recipes for sunscreen present an opportunity for public health professionals to proactively engage on social media. Abbreviations: US: United States; SPF: sun protection factor; USFDA: United states food and drug administration; UV: ultraviolet.

[Actinic keratoses : Current guideline and practical recommendations]

The S3 guideline "Actinic keratosis and squamous cell carcinoma of the skin" was published on 30 June 2019. Subsequently, publications, reviews and meta-analyses appeared with new questions regarding the comparability of study data and heterogeneity of the evaluations, which are caused, among other things, by divergent measurement parameters as well as insufficient consideration of pretreatments and combined treatments. This concise overview was written in the context of criticism and in view of necessary developments and research. Topics include epidemiology, pathogenesis, prevention, clinical presentation, therapy and BK5103. Therapy is divided into local destructive procedures and topical applications. Recommendations with quotation marks are based on the actual guideline. Corresponding evidence levels are given. For the implementation in daily routine basic data, side effects and features of therapeutic options are mentioned. The current developments and questions concerning actinic keratoses become clear.

Investigating partitioning of free versus macrocycle bound guest into a model POPC lipid bilayer

We report on the permeation of free and macrocycle-bound avobenzone across a POPC lipid bilayer through combined neutron reflectometry experiments and molecular dynamics simulations. Results indicate that the p-phosphonated calix[8]arene macrocycle limits the avobenzone penetration into the upper leaflet of the membrane. Hence, it could serve as a useful vehicle for safer formulations.

We report on the permeation of free and macrocycle-bound avobenzone across a POPC lipid bilayer through combined neutron reflectometry experiments and molecular dynamics simulations.

Towards symmetry driven and nature inspired UV filter design

In plants, sinapate esters offer crucial protection from the deleterious effects of ultraviolet radiation exposure. These esters are a promising foundation for designing UV filters, particularly for the UVA region (400 – 315 nm), where adequate photoprotection is currently lacking. Whilst sinapate esters are highly photostable due to a cis-trans (and vice versa) photoisomerization, the cis-isomer can display increased genotoxicity; an alarming concern for current cinnamate ester-based human sunscreens. To eliminate this potentiality, here we synthesize a sinapate ester with equivalent cis- and trans-isomers. We investigate its photostability through innovative ultrafast spectroscopy on a skin mimic, thus modelling the as close to true environment of sunscreen formulas. These studies are complemented by assessing endocrine disruption activity and antioxidant potential. We contest, from our results, that symmetrically functionalized sinapate esters may show exceptional promise as nature-inspired UV filters in next generation sunscreen formulations.

Sinapate esters are promising nature-inspired sunscreen and antioxidant agents but their photoisomerization may lead to ineffective or harmful species. Here the authors propose a symmetric ester with indistinguishable trans and cis isomers and prove its effectiveness by optical spectroscopies on a skin mimic.

Sunscreen Use and Melanoma Risk Among Young Australian Adults

Importance

There are limited data among young adults on sunscreen use during childhood and adulthood and on the association of sunscreen use with melanoma risk.

Objective

To assess correlates of early-life sunscreen use and the association between sunscreen use and risk of cutaneous melanoma before age 40 years.

Design, Setting, and Participants

This population-based, case-control family study analyzed Australian Melanoma Family Study data for persons with questionnaire data on sunscreen use collected by interview from 2001 to 2005 across 3 states in Australia, representing two-thirds of the country's population. Case participants (aged 18-39 years) had confirmed first primary melanoma. Siblings of case participants were included, and case participants without a sibling control were excluded. Unrelated controls (aged 18-44 years) were recruited from the electoral roll or were a spouse, partner, or friend nominated by case participants. Data analyses were conducted from October 2017 to February 2018.

Exposures

Self- and parent-reported sunscreen use, sun exposure, and other candidate risk factors during childhood and adulthood.

Main Outcomes and Measures

Logistic regression analyses adjusted for potential confounders were used to estimate odds ratios (ORs) for melanoma and for correlates of sunscreen use.

Results

Participation was 629 of 830 contactable cases (76%) (629 of 1197 overall [53%]), 240 of 570 contactable controls (42%) from the electoral roll (240 of 1068 overall [23%]), and 295 of 371 nominated spouse or friend controls (80%); analysis incuded 603 cases and 1088 controls. The median (interquartile range) age was 32 (28-36) years for 603 cases, 35 (30-38) years for 478 unrelated controls, and 34 (29-38) years for 610 sibling controls. There were more women than men (range, 57%-62%) in all groups, approximately 40% (range, 39%-43%) of participants had a university education, and most participants (range, 58%-73%) had British/northern European ethnicity. Risk of melanoma was less with higher use of sunscreen in childhood (OR for highest vs lowest tertiles, 0.60; 95% CI, 0.42-0.87; P = .02 for trend) and across the lifetime (OR, 0.65; 95% CI, 0.45-0.93; P = .07 for trend). Subgroup analyses suggested that the protective association of sunscreen with melanoma was stronger for people reporting blistering sunburn, receiving a diagnosis of melanoma at a younger age, or having some or many nevi. Total lifetime sun exposure was unrelated to melanoma risk (OR for highest vs lowest tertile, 0.97; 95% CI, 0.66-1.43; P = .94 for trend). By contrast, total sun exposure inversely weighted by sunscreen use (as a measure of sun exposure unprotected by sunscreen) was significantly associated with melanoma risk (OR, 1.80; 95% CI, 1.22-2.65; P = .007 for trend) and appeared stronger for people having lighter pigmentation or some or many nevi or using sunscreen to stay longer in the sun. Regular users of sunscreen were more likely to be female, younger, and of British or northern European ancestry and to have higher educational levels, lighter skin pigmentation, and a stronger history of blistering sunburn.

Conclusions and Relevance

Our findings provided evidence that regular sunscreen use is significantly associated with reduced risk of cutaneous melanoma among young adults and identified several characteristics associated with less sunscreen use.

Saccharomyces cerevisiae strains as bioindicators for titanium dioxide sunscreen photoprotective and photomutagenic assessment

Although several short-term assays are available for cosmetic photosafety assessment, cell models are usually highly sensitive to UV radiation, tending to overestimate both phototoxic and photomutagenic risks. In addition, these assays are performed with UV doses/fluences that do not correspond to actual environmental conditions. In this sense, Saccharomyces cerevisiae has already proved to be an interesting tool to predict photomutagenic potential of several compounds, including sunscreens. Yeast can support environmental UVB doses compatible with human daily sunlight exposure, allowing the use of irradiation sources to faithfully mimic the external conditions of ambient sunlight. Herein, we used a set of S. cerevisiae mutant strains sensitive to UVA, UVB and Solar Simulated Light sources in order to evaluate their potential as bioindicators for sunscreen development. The bioindicator potential of the strains was tested with the widely-used titanium dioxide inorganic sunscreen. The AWP001 (yno1) and LPW002 (ogg1yno1) strains obtained in this study stood out as promising experimental tools for the validation of this assay. Overall, our results evidenced a set of S. cerevisiae strains particularly useful for evaluating both photoprotective (efficacy) and photo/antiphotomutagenic (safety) potential of UV filters, meeting the industries and regulatory agencies demand for robust and efficient in vitro screening tests.

Mapping the intrinsic absorption properties and photodegradation pathways of the protonated and deprotonated forms of the sunscreen oxybenzone

Sunscreens provide vital protection against the photodamaging effects of UV radiation, however, many fundamental questions remain about the detailed mechanisms by which they dissipate UV energy. One such issue is the extent to which the pH environment of an organic sunscreen molecule alters its effectiveness, both in terms of ability to absorb UV radiation, and also its potential to photodegrade. Here, we use gas-phase laser photodissociation spectroscopy for the first time to measure the intrinsic UVA-UVC absorption spectra and associated photodegradation products of protonated and deprotonated oxybenzone, away from the complications of bulk mixtures. Our results reveal that protonation state has a dramatic effect on the absorption and photodissociation properties of this sunscreen. While the UV absorption profile of oxybenzone is only modestly affected by protonation across the range from 400-216 nm, deprotonated oxybenzone displays a significantly modified absorption spectrum, with very low photoabsorption between 370-330 nm. Protonated oxybenzone primarily photofragments by rupture of the bonds on either side of the central carbonyl group, producing cationic fragments with m/z 151 and 105. Additional lower mass photofragments (e.g. m/z 95 and 77) are also observed. The production spectra for the photofragments from protonated oxybenzone fall into two distinct categories, which we discuss in the context of different excited state decay pathways. For deprotonated oxybenzone, the major photofragments observed are m/z 211 and 212, which are associated with the ejection of methane and the methyl free radical from the parent ion, respectively. Implications for the suitability of oxybenzone in its protonated and deprotonated forms as an optimum sunscreen molecule are discussed.

Biodistribution, Clearance, and Long-Term Fate of Clinically Relevant Nanomaterials

Realization of the immense potential of nanomaterials for biomedical applications will require a thorough understanding of how they interact with cells, tissues, and organs. There is evidence that, depending on their physicochemical properties and subsequent interactions, nanomaterials are indeed taken up by cells. However, the subsequent release and/or intracellular degradation of the materials, transfer to other cells, and/or translocation across tissue barriers are still poorly understood. The involvement of these cellular clearance mechanisms strongly influences the long-term fate of used nanomaterials, especially if one also considers repeated exposure. Several nanomaterials, such as liposomes and iron oxide, gold, or silica nanoparticles, are already approved by the American Food and Drug Administration for clinical trials; however, there is still a huge gap of knowledge concerning their fate in the body. Herein, clinically relevant nanomaterials, their possible modes of exposure, as well as the biological barriers they must overcome to be effective are reviewed. Furthermore, the biodistribution and kinetics of nanomaterials and their modes of clearance are discussed, knowledge of the long-term fates of a selection of nanomaterials is summarized, and the critical points that must be considered for future research are addressed.

Photoprotection: extending lessons learned from studying natural sunscreens to the design of artificial sunscreen constituents

Evolution has ensured that plants and animals have developed effective protection mechanisms against the potentially harmful effects of incident ultraviolet radiation (UVR). Tanning is one such mechanism in humans, but tanning only occurs post-exposure to UVR. Hence, there is ever growing use of commercial sunscreens to pre-empt overexposure to UVR. Key requirements for any chemical filter molecule used in such a photoprotective capacity include a large absorption cross-section in the UV-A and UV-B spectral regions and the availability of one or more mechanisms whereby the absorbed photon energy can be dissipated without loss of the molecular integrity of the chemical filter. Here we summarise recent experimental (mostly ultrafast pump-probe spectroscopy studies) and computational progress towards unravelling various excited state decay mechanisms that afford the necessary photostability in chemical filters found in nature and those used in commercial sunscreens. We also outline ways in which a better understanding of the photophysics and photochemistry of sunscreen molecules selected by nature could aid the design of new and improved commercial sunscreen formulations.

From fundamental science to product: a bottom-up approach to sunscreen development

Despite the pivotal role of ultraviolet (UV) radiation in sustaining life on Earth, overexposure to this type of radiation can have catastrophic effects, such as skin cancer. Sunscreens, the most common form of artificial protection against such harmful effects, absorb UV radiation before it reaches vulnerable skin cells. Absorption of UV radiation prompts ultrafast molecular events in sunscreen molecules which, ideally, would allow for fast and safe dissipation of the excess energy. However, our knowledge of these mechanisms remains limited. In this article, we will review recent advances in the field of ultrafast photodynamics (light induced molecular processes occurring within femtoseconds, fs, 10-15 s to picoseconds, ps, 10-12 s) of sunscreens. We follow a bottom-up approach to common sunscreen active ingredients, analysing any emerging trends from the current literature on the subject. Moreover, we will identify the main questions that remain unanswered, pinpoint some of the main challenges and finally comment on the outlook of this exciting field of research.

Sunscreens: An Update

Sunscreens have been widely used by the general public for their photoprotective properties, including prevention of photocarcinogenesis and photoaging and management of photodermatoses. It is important to emphasize to consumers the necessity of broad-spectrum protection, with coverage of both ultraviolet A (320-400 nm) and ultraviolet B (290-320 nm) radiation. This review discusses the benefits of sunscreen, different ultraviolet filters, sunscreen regulations and controversies, the importance of broad-spectrum protection, issues of photostability and formulation, and patient education and compliance.

Ultrafast Transient Absorption Spectroscopy of the Sunscreen Constituent Ethylhexyl Triazone

The ultrafast photoprotection mechanisms in operation in ethylhexyl triazone (EHT, octyl triazone), an approved ultraviolet-B (UV-B) chemical filter for commercial sunscreens, remain elusive, with a notable absence of ultrafast time-resolved measurements. These large organic molecules are of increasing interest as they are suspected to be less likely to penetrate the skin than some of the smaller approved filters, thereby reducing the possible adverse effects from sunscreen products. We apply femtosecond transient absorption spectroscopy with electronic structure calculations to unravel the complete photodeactivation mechanism that EHT undergoes after UV-B irradiation. We propose that this involves ultrafast internal conversion of the initially photoexcited n¹ππ* state that couples to the ground state via a 1¹ππ*/S₀ conical intersection, enabling multiple absorption and recovery cycles, as one would anticipate from a highly efficient filter. We also observe long-lived photoproducts which, based on previous studies along with present electronic structure calculations, we attribute to trapped excited populations in the S₁ and T₁ states.

A Perspective on the Ultrafast Photochemistry of Solution-Phase Sunscreen Molecules

Sunscreens are one of the most common ways of providing on-demand additional photoprotection to the skin. Ultrafast transient absorption spectroscopy has recently proven to be an invaluable tool in understanding how the components of commercial sunscreen products display efficient photoprotection. Important examples of how this technique has unravelled the photodynamics of common components are given in this Perspective, and some of the remaining unanswered questions are discussed.

A Way Forward for Cancer Chemoprevention: Think Local

As cells progress through carcinogenesis, the associated exponential expansion of genetic and molecular aberrations and resultant heterogeneity make therapeutic success increasingly unattainable. Therapeutic intervention at early stages of carcinogenesis that occurs within the primary organ and in the face of a lower burden of molecular aberrations, constitutes a basic tenet of cancer chemoprevention, and provides a situation that favors a greater degree of therapeutic efficacy compared with that of advanced cancer. A longstanding barrier to chemoprevention relates to the requirement for essentially no systemic toxicity, and the fact that when large numbers of people are treated, the emergence of systemic toxicity is almost universal. A rational means to address this in fact relates to a second basic tenet of the chemopreventive strategy: the focus of therapeutic intervention is to disrupt a process that is in essence localized to a single organ. Based upon this consideration, a strategy which is based upon local delivery of therapeutics to an at-risk organ will achieve therapeutic efficacy while avoiding systemic delivery and its associated toxicity. This article will review the rationale for undertaking such an approach, describe successful clinical achievements based on this strategy, describe ongoing efforts to expand the impact of this approach, and together will highlight the high impact that this approach has already had on the field as well as its extremely high potential for future impact. Cancer Prev Res; 10(1); 14-35. ©2016 AACR.

Ultraviolet radiation and effects on humans: the paradigm of maternal vitamin D production during pregnancy

Current evidence indicates that neonates born of mothers with vitamin D deficiency during pregnancy have greater risk for developing hypocalcemia, rickets and extra-skeletal disorders. Despite the classic knowledge that ultraviolet-B (UVB) exposure is the most efficient way for a future mother to obtain optimal vitamin D concentrations, no current consensus or clinical recommendations exist regarding the duration and timing of UVB exposure for pregnant women. This article offers a narrative review of available data regarding how UVB exposure affects maternal vitamin D production during pregnancy, along with a discourse on clinical implications of this public health issue. Future studies would benefit from adopting UVB exposure estimates to recommend appropriate UVB exposure to pregnant women. Doing so could provide a more holistic and practical approach in managing maternal hypovitaminosis D during pregnancy.

Observing and understanding the ultrafast photochemistry in small molecules: applications to sunscreens

In this review, we discuss the importance of biological and artificial photoprotection against overexposure to harmful ultraviolet radiation. Transient electronic and transient vibrational absorption spectroscopies are highlighted as important tools in understanding the energy transfer in small molecules, with a focus on the application to commercial sunscreens with representative examples given. Oxybenzone, a common ingredient in commercial sunscreens and sinapoyl malate, a biological sunscreen in plant leaves are presented as case studies.

Photodynamics of potent antioxidants: ferulic and caffeic acids

The dynamics of ferulic acid (3-(4-hydroxy-3-methoxyphenyl)-2-propenoic acid) and caffeic acid (3-(3,4-dihydroxyphenyl)-2-propenoic acid) in acetonitrile, dioxane and water at pH 2.2 following photoexcitation to the first excited singlet state are reported. These hydroxycinnamic acids display both strong ultraviolet absorption and potent antioxidant activity, making them promising sunscreen components. Ferulic and caffeic acids have previously been shown to undergo trans-cis photoisomerization via irradiation studies, yet time-resolved measurements were unable to observe formation of the cis-isomer. In the present study, we are able to observe the formation of the cis-isomer as well as provide timescales of relaxation following initial photoexcitation.

Ultrafast photoprotective properties of the sunscreening agent octocrylene

Today octocrylene is one of the most common molecules included in commercially available sunscreens. It provides broadband photoprotection for the skin from incident UV-A and UV-B radiation of the solar spectrum. In order to understand how octocrylene fulfils its role as a sunscreening agent, femtosecond pump-probe transient electronic UV-visible absorption spectroscopy is utilised to investigate the ultrafastnonradiative relaxation mechanism of octocrylene in cyclohexane or methanol after UV-B photoexcitation. The data presented clearly shows that UV-B photoexcited octocrylene exhibits ultrafast-nonradiative relaxation mechanisms to repopulate its initial ground state within a few picoseconds, which, at the very least, photophysically justifies its wide spread inclusion in commercial sunscreens.