Change of ultraviolet absorbance of sunscreens by exposure to solar-simulated radiation

Sun protection, progress, myths, and inconsistencies (a proposal for the democratization of ISO 24443)

The concept of modern human sun protection is no more than one hundred years, but real development of it, including protection against UVA + UVB radiation (and more recently also the IR and blue light), has been no more than 30 years. One fundamental issue while formulating sunscreens is the photostability of the UV filters, which is particularly feeble for the UVA. The gold standard for the determination of sunscreen UVA protection "in vitro" is ISO 24443:2021. Still, interlaboratory results are not as consistent as expected. The Technical Committee for Cosmetics (ISO TC 217) has tried to standardize the method with precise specifications for the materials and equipment used. In particular, the standardization of UV exposure sources based on Xe arc lamps. This fact requires expensive equipment out of the reach of many laboratories to achieve adequate temperature control on the samples. In this paper, it will be shown that, within the experimental error, satisfactory results were achieved with a cheap commercial LED source irradiating only in the UVA spectra. Evidence is presented to conclude that other more relevant factors must be considered as the main cause of uncertainties.

Degradation studies of UV filter hexyl 2-[4-(diethylamino)-2-hydroxybenzoyl]-benzoate (DHHB) in aqueous solution

High performance liquid chromatography coupled with ultra-violet, diode array detection (HPLC-UV-DAD), was used to study the degradation reactions of ultraviolet (UV) filter hexyl 2-[4-(diethylamino)-2-hydroxybenzoyl]-benzoate (DHHB). Degradation by-products were detected and identified by means of liquid chromatography coupled with diode array detection and mass spectrometry (LC-DAD-MS). Environmentally-relevant characteristics, such as water pH, chlorine levels, water temperature and dissolved organic matter (DOM) concentration, were modulated and studied in order to determine their influence on the degradation reactions. Results show that DHHB degrades quite rapidly in typical drinking water disinfection conditions, displaying a kinetic rate constant of k_obs = 0.0060 ± 0.0002 s^-1 and a half-life period of merely t_1/2 = 116 ± 4 s. As far as the non-volatile disinfection by-products (DBPs) are concerned, only the mono and dichlorinated forms of DHHB were detected in the degradation reactions. Regarding influential variables on DHHB degradation, the presence or absence of DOM in solution did not alter the trends that were found (degradation of DHHB is more significant at lower pH values and higher levels of active chlorine in solution). Chlorinated DBPs have also been found to predominate under higher pH values and lower levels of chlorine, whereas they were found to be unstable and further degradable, quite likely into smaller and more volatile compounds, when in lower pH and higher chlorine concentrations. As for the photo-degradation studies, DHHB was found to be extremely photo-stable, with only about 15% degradation rate detected during artificial irradiation periods of 6 h.

Suboptimal UVA attenuation by broad spectrum sunscreens under outdoor solar conditions contributes to lifetime UVA burden

BACKGROUND

Broad spectrum sunscreens with a sun protection factor (SPF) of 15 or greater are indicated to decrease the risk of skin cancer and early skin aging caused by the sun if used as directed with other sun protection measures. To determine whether sunscreen product performance is compromised under solar exposure and to test spectral uniformity of protection across the UVA spectrum, we tested broad spectrum sunscreens with a variety of active pharmaceutical ingredients (APIs) and in a variety of dosage forms.

METHODS

A cross-sectional market survey of 32 sunscreen drug products containing either organic or inorganic APIs with SPFs of 15, 30, 50, and 70 was tested. UV doses were delivered via natural sun in Silver Spring, Maryland between June and September of 2017.

RESULTS

Of the 32 sunscreen drug products, 6 products failed to meet their broad spectrum claim under solar exposure. Using FDA's new proposal to strengthen sunscreen broad spectrum requirements, spectral uniformity based on the mean sunscreen absorbance of UVA1(340-400 nm)/UV (290-400 nm) indicated that ~40% of sunscreen drug products tested had suboptimal UVA protection.

CONCLUSION

US consumers may unknowingly be receiving up to 36% more transmitted UVA when selecting between similarly labeled broad spectrum sunscreen drug products with equivalent SPF values. FDA's new proposal may help decrease consumers' overall lifetime UVA burden. Spectral absorbance data on sunscreen performance can be used to further improve the coupling of broad spectrum protection to a product's SPF value so that consumers have improved proportional increases in UV protection.

Development of broad spectrum mycosporine loaded sunscreen formulation from Ulva fasciata delile

Ba.ckground: Sunscreen formulations primarily offer protection against UV induced damages however nowadays it also maintains skin natural physiological conditions. Current global market is flooded with numerous sunscreen products which offer protection to skin against several UV induced damages. However most of these sunscreen formulations offers narrow spectrum protection against UV and also suffer from stability as well as toxicity related issues.

Methods: Present work aims to isolate mycosporine amino acid (Mgy) from green alga namely Ulva fasciata (U. fasciata) and study its sunscreen potential against widely used domestic marketed formulation. Stability evaluations were also performed for almost 90 days.

Results: Results demonstrated that the isolated compound, mycosporine glycine (Mgy) preserved physicochemical properties of the product and offered good stability for all formulations throughout the experimental period. Furthermore, Mgy loaded carbopol gel showed better sunscreen protection against marketed formulation in a concentration dependent manner. (7.709).

Conclusion: (6.806) Novel Myg loaded gel was proved to demonstrate several quality characteristics that may unlock new prospects for the production of more efficient, safe, and economic skin-care products.

Molecular photoprotection of human keratinocytes in vitro by the naturally occurring mycosporine-like amino acid palythine

Background

Solar ultraviolet radiation (UVR) induces molecular and genetic changes in the skin, which result in skin cancer, photoageing and photosensitivity disorders. The use of sunscreens is advocated to prevent such photodamage; however, most formulations contain organic and inorganic UVR filters that are nonbiodegradable and can damage fragile marine ecosystems. Mycosporine‐like amino acids (MAAs) are natural UVR‐absorbing compounds that have evolved in marine species for protection against chronic UVR exposure in shallow‐water habitats.

Objectives

To determine if palythine, a photostable model MAA, could offer protection against a range of UVR‐induced damage biomarkers that are important in skin cancer and photoageing.

Methods

HaCaT human keratinocytes were used to assess the photoprotective potential of palythine using a number of end points including cell viability, DNA damage (nonspecific, cyclobutane pyrimidine dimers and oxidatively generated damage), gene expression changes (linked to inflammation, photoageing and oxidative stress) and oxidative stress. The antioxidant mechanism was investigated using chemical quenching and Nrf2 pathway activation assays.

Results

Palythine offered statistically significant protection (P < 0·005) against all end points tested even at extremely low concentrations (0·3% w/v). Additionally, palythine was found to be a potent antioxidant, reducing oxidatively generated stress, even when added after exposure.

Conclusions

Palythine is an extremely effective multifunctional photoprotective molecule in vitro that has potential to be developed as a natural and biocompatible alternative to currently approved UVR filters.

What's already known about this topic?

Mycosporine‐like amino acids (MAAs) are photoprotective molecules found in marine organisms but there are few data on their ability to protect skin cells from the adverse effects of solar ultraviolet radiation (UVR).

The European Chemicals Agency (ECHA) is concerned about the potential adverse health and ecotoxic effects of eight of 16 commonly used sunscreen filters in Europe. The Environmental Effects Assessment Panel (EEAP) of the United Nations Environment Programme has expressed similar concerns.

What does this study add?

Palythine, an MAA extracted from an edible seaweed, affords photoprotection against a wide range of adverse effects in HaCaT keratinocytes exposed to solar simulating and ultraviolet A radiation. Of note is protection against two types of DNA photolesions; cyclobutane pyrimidine dimers and 8‐oxo‐7,8‐dihydroguanine.

Palythine is also a potent antioxidant that offers protection even when added after UVR exposure.

What is the translational message?

MAAs should be considered for development as natural biocompatible sunscreens that may address the concerns of the ECHA and EEAP.

Linked Comment: https://doi.org/10.1111/bjd.16598.

https://goo.gl/Uqv3dl

Natural Substances for Prevention of Skin Photoaging: Screening Systems in the Development of Sunscreen and Rejuvenation Cosmetics

Solar broadband UV irradiation is commonly regarded as a major causative reason for cutaneous photoaging. The pro-aging molecular pathways and cellular targets affected by UVA+UVB light in human skin have been extensively investigated. Notwithstanding growing knowledge in mechanisms of photoaging, research and development of clinically efficient, nontoxic, and sustainable topical preparations providing full physical, chemical, and biological photoprotection still remain a great challenge for pharmaceutical and cosmetic industries. In this study, we are proposing a panel of the in vitro methods for preselection of natural photoprotective substances with high photostability and low phototoxicity able of absorbing a broadband UVA+UVB irradiation (physical sunscreen), reducing UV-related overproduction of free radicals and loss of endogenous antioxidants (chemical protection), and attenuating UV-induced cytotoxicity and immune and metabolic responses (biological protection) in primary human epidermal keratinocytes and immortalized human keratinocyte cultures. Our data showed that secondary metabolites biosynthesized in plant cells in response to UV irradiation, such as phenylpropanoids and their glycosylated metabolites, aglycons and glycosylated flavonoids, and leontopodic acids, hold the best promise for complete natural topical prevention of photoaging and rejuvenation of photoaged skin. Meristem plant cell cultures elicited by solar simulating UV could be the most environmentally sustainable biotechnological source of polyphenols with combined photoprotective and antiaging properties.

Cutaneous biocompatible rutin-loaded gelatin-based nanoparticles increase the SPF of the association of UVA and UVB filters

The encapsulation of natural ingredients, such as rutin, can offer improvements in sun protection effectiveness. This strategy can provide enhanced flavonoid content and produces an improved bioactive compound with new physical and functional characteristics. As an alternative to common synthetic-based sunscreens, rutin-entrapped gelatin nanoparticles (GNPs) were designed and associated with ethylhexyl dimethyl PABA (EHDP), ethylhexyl methoxycinnamate (EHMC) and methoxydibenzoylmethane (BMDBM) in sunscreen formulations. The purpose of this study was to develop rutin-loaded gelatin nanoparticles and characterize their physicochemical, thermal, functional and safety properties. Rutin-loaded gelatin nanoparticles increased antioxidant activity by 74% relative to free-rutin (FR) solution. Also, this new ingredient upgraded the Sun Protection Factor (SPF) by 48%, indicating its potential as a raw material for bioactive sunscreens. The safety profile indicated that GNPs and glutaraldehyde (GTA) decreased HaCaT cell viability in a concentration/time-dependent manner. However, both blank nanoparticles (B-NC) and rutin-loaded nanoparticles (R-NC) had good performance on skin compatibility tests. These results functionally characterized rutin-loaded nanoparticles as a safe SPF enhancer in sunscreens, especially in association with UV filters.

Broad-spectrum sun-protective action of Porphyra-334 derived from Porphyra vietnamensis

There are enormous UV-protective compounds present in the current world market, out of which 98% give protection against UV-B range and the remaining 2% are potent against far UV-A range only. Furthermore, these synthetic compounds have various problems related to photo-stability and cross-stability. There is a vital need of sunscreen agents that will remain stable for prolonged periods and provide broad-spectrum protection against harmful UV range. The Indian Ocean contains large amounts of macro-algae which synthesize varied amount of mycosporine amino acids, "sun-protective compounds" by shikmic acid pathway. In the present study, we have evaluated the sunscreen protection provided by Porphyra-334, a mycosporine amino acid isolated from Indian sp. of Porphyra. Furthermore, the isolated compound was detected by high performance thin layer chromatography (HPTLC) fingerprinting, high performance liquid chromatography (HPLC) and ultraviolet (UV), whereas nuclear magnetic resonance (NMR) spectroscopy and infrared spectrometry were used for its structural characterization. Stability studies were performed under different storage and pH conditions. Ultimately a sunscreen formulation was developed and its potential against marketed Aloe vera gel was evaluated by in vitro sunscreen protection method. It was observed that sunscreen potential of Porphyra-334 was 5.11-fold greater than that of the marketed Aloe vera gel preparation.

Development of a new in vitro method to evaluate the photoprotective sunscreen activity of plant extracts against high UV-B radiation

Sunscreen efficiency of biomolecules against UV-B radiation was generally determined in vitro by cosmetic methods which are not well-adapted for routine ecophysiological and bio-guidance studies in plant research laboratories. In this article, we propose a new in vitro method to evaluate the sunscreen photoprotective activity of plant extracts against high UV-B radiation. Because photosynthetic pigments are one of the first targets of UV-B radiation in plants, the experimental design is based on the ability of the tested substances to limit the degradation of sodium magnesium chlorophyllin (SMC), a derivative compound of natural chlorophyll. SMC photodegradation comparatively to natural chlorophyll and related to temperature, concentration and sample solvent were analyzed in order to optimize the experimental parameters. Then, the method was validated by testing nine standard UV filters used in the European cosmetic industry and by comparing results of their activity with those of a reference in vitro procedure. Finally, the method was applied to coastal and marine crude plant extracts. Results have shown that our procedure can be a good alternative to cosmetic methods with a rapid, sensitive and reproducible evaluation of the sunscreen activity of either pure standards or crude plant extracts in small amounts (30 mg).

Characterization of the UVA protection provided by avobenzone, zinc oxide, and titanium dioxide in broad-spectrum sunscreen products

BACKGROUND

Solar UV radiation (UVR) is composed of UVB (290-320 nm) and UVA (320-400 nm) wavelengths. Only two sunscreen active ingredients approved in the US, avobenzone (butylmethoxydibenzoylmethane) and zinc oxide (ZnO), provide true broad-spectrum protection against UVA wavelengths >360 nm. Although effective against shorter UVR wavelengths <360 nm, titanium dioxide (TiO(2)) is also often believed to confer broad-spectrum protection and is substituted for ZnO or avobenzone. To sustain its absorption capacity within a sunscreen film during UVR exposure, avobenzone needs to be formulated into sunscreen products using sound formulation strategies.

OBJECTIVES

To characterize the efficacy of avobenzone, ZnO, and TiO(2) in terms of their abilities to provide broad UVA protection and to demonstrate the effectiveness of the different formulation strategies used today to maintain the efficacy of avobenzone even during prolonged exposures to UVR.

METHODS

UVA efficacy was assessed by measuring absorbance profiles in vitro using Vitro Skin® (IMS Inc., Orange, CT, USA) as an inert substrate and by determining UVA protection factors (PFA) on human skin. The impact of avobenzone loss on sun protection factor (SPF) and PFA values was evaluated by serially reducing avobenzone concentrations in an otherwise photostable product. The photostabilizing influence of specific formulation ingredients was monitored by measuring the extent to which they prevented UVR-induced degradation of avobenzone, whereas photostability of commercial sunscreen products was quantified by measuring the percentage change in absorbance within the UVB and UVA spectral regions following irradiation of thin product films on inert substrates.

RESULTS

Model formulations containing 3% avobenzone or 5% ZnO provided superior attenuation of UVA wavelengths >360 nm compared with formulas containing 5% TiO(2). Additionally, sunscreen products of similar SPF containing avobenzone or ZnO exhibited significantly higher PFA values than those containing TiO(2). The addition of photostabilized avobenzone or ZnO increased PFA values nearly 3-fold, whereas the addition of TiO(2) increased PFA values only modestly. Judicious selection of sunscreen actives alone or in combination with extra stabilizing agents maintained the photostability of avobenzone in formulations to deliver sustained broad-spectrum absorbance during 4 hours of exposure to UVR. Small losses (<20%) of avobenzone did not significantly reduce a product's protective effects as measured by SPF and PFA values on human skin.

CONCLUSIONS

TiO(2) provided neither the same level of UVA attenuation nor the same degree of UVA protection on human skin as did products containing photostabilized avobenzone or ZnO. Hence, TiO(2) cannot be considered a substitute for avobenzone or ZnO in providing high levels of UVA protection to human skin. Use of proper formulation strategies can ensure that avobenzone losses are minimized to the extent that they have no impact on a product's ability to deliver sustained protection, even over periods of prolonged exposure to UVR.

Sunscreens and occupation: the Austrian experience

Since the nineteen fifties the attitude of the fair-skinned world population towards the sun has changed dramatically. Tanned skin, which before was regarded as the stigma of the underprivileged working classes, became fashionable and desirable. The science of photoprotection primarily focuses on ultraviolet exposure during leisure time activities, whereas ultraviolet radiation is still underestimated as a risk factor for UV-induced skin and eye problems. The actual discussion on the registration of UV-induced skin tumours as occupational diseases, however, has drawn more attention to this important issue. Ambient radiation, the working process itself and the photoprotective behaviour of an outdoor worker are the main factors which influence the actual UV exposure. However, the total risk for the development of actinic damage results from the interaction of both the occupational and the leisure time exposure. It is evident that there is a high need for photoprotective measures for outdoor workers. Topical sunscreens as a part of a comprehensive UV protection strategy for outdoor workers have to fulfil special requirements: reasonable price, high water resistance, non-sticky appearance. At present only a few products are available which meet these criteria. This is the reason why sunscreens are not so well accepted by outdoor workers. Great efforts have to be undertaken to improve sunscreen formulations and to convince people to apply them correctly and regularly.

Octyl methoxycinnamate modulates gene expression and prevents cyclobutane pyrimidine dimer formation but not oxidative DNA damage in UV-exposed human cell lines

Octyl methoxycinnamate (OMC) is one of the most widely used sunscreen ingredients. To analyze biological effects of OMC, an in vitro approach was used implying ultraviolet (UV) exposure of two human cell lines, a primary skin fibroblast (GM00498) and a breast cancer (MCF-7) cell lines. End points include cell viability assessment, assay of cyclobutane pyrimidine dimers (CPDs) and oxidated DNA lesions using alkaline elution and lesion-specific enzymes, and gene expression analysis of a panel of 17 DNA damage–responsive genes. We observed that OMC provided protection against CPDs, and the degree of protection correlated with the OMC-mediated reduction in UV dose. No such protection was found with respect to oxidative DNA lesions. Upon UV exposure in the presence of OMC, the gene expression studies showed significant differential changes in some of the genes studied and the expression of p53 protein was also changed. For some genes, the change in expression seemed to be delayed in time by OMC. The experimental approach applied in this study, using a panel of 17 genes in an in vitro cellular system together with genotoxicity assays, may be useful in the initial screening of active ingredients in sunscreens.

Photostabilization effect of quercetin on the UV filter combination, butyl methoxydibenzoylmethane-octyl methoxycinnamate

The aim of the study was to investigate the effect of the natural antioxidant quercetin on the photostability of the most widely used combination of UVA (320-400 nm) and UVB (290-320 nm) filters, respectively butyl methoxydibenzoylmethane (BMDBM) and octyl methoxycinnamate (OMC). In order to reproduce the conditions prevalent in commercial sunscreen products, the stabilizing efficacy of quercetin was evaluated in model creams containing BMDBM (3%, wt/wt) together with OMC (4%, wt/wt) and exposed to a solar simulator at an irradiance corresponding to natural sunlight. Quercetin was found to enhance the photostability of the two UV filters in a concentration-dependent way. Addition of quercetin to the sunscreen formulation significantly reduced the photodegradation of BMDBM and OMC from 40.3 +/- 2.4 to 27.7 +/- 2.6% and from 51.3 +/- 2.1 to 42.2 +/- 2.0%, respectively. Moreover, comparative photodegradation studies demonstrated that quercetin was much more effective and at a lower concentration than commonly used stabilizer (octocrylene) and antioxidants (vitamin E, butylated hydroxyanisole). In vitro determination of the UVB and UVA protection parameters showed that the quercetin-based formulation fulfilled the official requirements on sunscreen products. Because of its photostabilizing and multiple antioxidant properties, quercetin represents a useful additive for the formulation of effective broad-spectrum sunscreens containing BMDBM and OMC.

Comparative evaluation of different substrates for the in vitro determination of sunscreen photostability: spectrophotometric and HPLC analyses

Polymethylmethacrylate (PMMA) plates and Transpore(TM) tapes were compared as substrates for the in vitro evaluation of photostability of commercial sunscreen products. The sun care preparations were applied respectively on Transpore(TM) tapes and PMMA plates and their sun protection factors (SPF) and UVA protection parameters [UVA/UVB ratio, critical wavelength, UVA protection factor (UVA-PF)] were measured by transmission spectroscopy, before and after irradiation with simulated sunlight. No significant differences were observed in the UV protection parameters measured on Transpore(TM) tapes or PMMA plates, before exposure to the solar simulator. Conversely, after irradiation, the SPF values of the sun care products exhibited marked variations between the two substrates, the decrease in SPF being greater on PMMA plates (31.3-63.1%) than on Transpore(TM) tapes (10.4-23.8%). Differences between the two substrates were detected also for the UVA protection parameters, although they were significant only for the UVA-PF. The tested samples were assayed also by high-performance liquid chromatography (HPLC) to assess the extent of photodegradation of the UV filters present in the examined formulations. The results showed that for the PMMA plates, the light-induced decrease in SPF, as determined by spectrophotometry, fitted well with the percentage loss of ethyl hexyl methoxycinnamate (the only photounstable UVB filter present) measured by HPLC. Moreover, for the PMMA substrate, the UVA-PF percentage reduction was consistent with the percentage degradation of butyl methoxydibenzoylmethane (the only photounstable UVA filter present) determined by HPLC. On the other hand, poor correlation between spectrophotometric and HPLC analyses was observed on Transpore(TM) tapes. Therefore, PMMA plates are more reliable than Transpore(TM) tapes as substrates for in vitro photodegradation tests of sunscreen products by transmission spectroscopy.

Synthesis and application of a novel sunscreen-antioxidant

Background information on the inefficacy of sunscreens to provide free radical protection in skin, despite their usefulness in preventing sunburn/erythema, prompted us to synthesize a compound which would display in the same molecule both UV-absorbing and antioxidant capacities. For this purpose, the UVB absorber, 2-ethylhexyl-4-methoxycinnamate (OMC) was combined with the piperidine nitroxide TEMPOL, which has antioxidant properties. The spectral properties of the new nitroxide-based sunscreen (MC-NO) as well as its efficacy to prevent photo-oxidative damage to lipids induced by UVA, natural sunlight and 4-tert-butyl-4-methoxydibenzoylmethane (BMDBM), a photo-unstable sunscreen which generates free radicals upon UV radiation, was studied. The results obtained demonstrate that MC-NO: (a) absorbs in the UVB region even after UVA irradiation; (b) acts as free radical scavenger as demonstrated by EPR experiments; (c) strongly reduces both UVA-, sunlight- and BMDBM-induced lipid peroxidation in liposomes, measured as reduced TBARS levels; and (d) has comparable antioxidant activity to that of commonly used vitamin E and BHT in skin care formulations. These results suggest that the use of the novel sunscreen-antioxidant or of other nitroxide-based sunscreens in formulations aimed at reducing photoinduced skin damage may be envisaged.

[UV Filters. State of the art]

This article describes the basic principles of photoprotection with classic sunscreens containing chemical and/or physical UV filters and standard methods of sun protection factor (SPF) determination. In addition, the new governmental regulations and recommendations of the European Commission for photoprotection are presented and compared to regulations in other regions of the world. Finally, the efficacy of sunscreens in sunlight-induced non-sunburn effects, such as immune suppression and carcinogenesis are discussed.

Changes in common melanocytic naevi after intense sun exposure: digital dermoscopic study with a 1-year follow-up

BACKGROUND

Exposure to ultraviolet (UV) radiation induces acute changes in common melanocytic naevi (CMN).

AIM

To analyse changes in size and dermoscopic structures of CMN in healthy individuals under the influence of intense sun exposure and to investigate effectiveness of sunscreen usage in preventing the appearance of dermoscopic changes.

METHODS

The subjects were divided into an SS group and a non-SS group, according to whether they used sunscreen or not. Digital epiluminiscence microscopy (DELM) was performed before sun exposure and 28 days and 1 year after the cessation of intense sun exposure.

RESULTS

Eleven subjects with 60 naevi fulfilled the inclusion criteria. A significant increase in one diameter of the CMN was found 28 days after cessation of sun exposure, irrespective of sunscreen usage. There was no significant change in total dermoscopy score during the follow-up period in either the SS or non-SS group. There were definitive DELM changes at the 1-year follow-up in 10% of CMNs < 5 mm in size. Changes in pigmented network, globules and streaks were fully reversible in the remaining CMN. The use of sunscreen had no influence on these changes.

CONCLUSIONS

The increases in the size of melanocytic naevi that we found 28 days after cessation of intense sun exposure are probably induced by UV radiation, whereas changes in DELM features that were not reversible in some small naevi at the 1-year follow-up could be related both to sun exposure and to the natural evolution of the naevi. The use of sunscreen does not seem to prevent these changes. Small naevi in low-risk young and middle-aged patients seem to be more prone to sun-induced DELM changes.

In vitro photostability and photoprotection studies of a novel 'multi-active' UV-absorber

This paper reports on the synthesis and properties of a new UV-absorber (OC-NO) based on the most popular UV filter worldwide, ethylhexyl methoxycinnamate (OMC) in which the methoxy group has been replaced with a pyrrolidine nitroxide bearing antioxidant activity. This sunscreen active has therefore both UV-absorbing and antioxidant properties which could ideally address both the UV-B and UV-A skin photo-damage. For broad-spectrum coverage, the combinations of OC-NO with two commonly used UV-A absorbers (BMDBM and DHHB) were also studied. The results obtained reveal that OC-NO: (a) is as photostable as OMC after UV-A exposure; (b) acts as free radical scavenger as demonstrated by EPR and chemical studies; (c) reduces UV-A and UV-A+BMDBM induced lipid peroxidation in liposomes and cells, measured as reduced TBARS levels and increased C11-BODIPY red fluorescence, respectively; (d) has comparable antioxidant activity to that of vitamin E and BHT commonly used in skin care formulations; (e) is non-cytotoxic to human skin fibroblasts as assessed with the MTT assay when exposed to increasing doses of UV-A; and (f) OC-NO+DHHB is a promising, photostable broad spectrum UV-filter combination that concomitantly reduces UV-induced free radical damage. These results suggest that nitroxide/antioxidant-based UV-absorbers may pave the way for the utilization of 'multi-active' ingredients in sunscreens thereby reducing the number of ingredients in these formulations.

Fluorescence dynamics of three UV-B sunscreens

Polarity of the surrounding medium affects the excited states of UV-B sunscreens. Therefore understanding excited state processes in a mixed polarity model system similar to skin is essential. We report the excited state lifetimes, quantum yields, radiative and non-radiative rates of three sunscreens. Among the three UV-B sunscreens studied, octyl salicylate emits from a single excited state, while padimate O and octyl methoxy cinnamate show multiple states. The radiative rates of salicylate and cinnamate are approximately constant, while that of padimate O depends strongly on solvent. The non-radiative rates of all sunscreens vary with solvent polarity. Compared to salicylate and cinnamate, padimate O is complex to analyze because of its two emission peaks and one peak's strong dependence on the dielectric constant. High absorbance, broad absorption peak with small fluorescence quantum yield, and low radiative rate make octyl methoxy cinnamate a superior UV-B sunscreen ingredient. The complexity in excited-state analysis shows that the lifetimes of the sunscreens are critical parameters, in addition to absorbance and quantum yield. Fluorescence lifetime substantiates the use of polystyrene nanospheres as a model host to study the photo-physical properties of sunscreen in a heterogeneous environment.

Quantification of ultraviolet protective effects of pityriacitrin in humans

Pityriacitrin (PIT), produced by Malassezia yeasts, is an UV absorbing substance that might cause hypopigmentation in pityriasis versicolor alba. We aimed to investigate the UV protective effect of PIT in humans using in vitro and in vivo test methods. Spectrophotometry of PIT cream and the vehicle was performed in the wavelength range from 290 to 400 nm. UV transmission and the sun protection factor (SPF) were assessed for different cream formulations. Using colorimetry we evaluated erythema and pigmentation following irradiation of cream-protected and non-protected skin of healthy subjects. UVB as well as UVA transmission decreased with increasing PIT concentrations. An increase of PIT concentration of 1.25, 2.5, and 5% was associated with slightly increasing SPFs of 1.4, 1.5, and 1.7, respectively. Our in vivo tests confirmed the validity of the SPF of PIT 5% cream determined in vitro. In conclusion, the UV protective effect of PIT is all in all very weak suggesting that PIT is likely only an inferior cofactor in the development of hypopigmentation in pityriasis versicolor alba lesions following sun exposure.

Fluorescence of sunscreens adsorbed to dielectric nanospheres: parallels to optical behavior on hacat cells and skin

Sunscreens applied to the skin are retained primarily in the stratum corneum, where they adsorb and act as a barrier preventing UV penetration to deeper layers. Photophysical properties of sunscreens have traditionally been studied either in solvents, which are very different from skin, or in skin or complex artificial skin systems, which are difficult to handle. The purpose of this study was to determine whether polystyrene nanospheres could serve as an improvement over solvents for evaluation of the photophysical properties of sunscreens without the presence of autofluorescence from and interactions with specific skin biomolecules. We used HaCat cells and excised skin for this comparative study with nanospheres. Fluorescence spectral properties of common hydrophobic sunscreens octyl salicylate, padimate O (2-ethylhexyl-4-dimethylaminobenzoate) and octyl methoxycinnamate adsorbed to 220 nm polystyrene spheres are similar to those of sunscreens adsorbed to HaCat cells and excised skin. Specifically, similarity in the emission peaks and their approximate positions, excitation peak positions and a measurable reduction in scattering upon sunscreen addition suggest that polystyrene nanospheres constitute a useful system to evaluate the photophysical properties of topical sunscreens and may serve as a model system for high-throughput evaluation of potential sunscreens. An unexpected result of this comparative study was the observation of an increase in a specific skin component emission caused by addition of padimate O.

A new method to test the effectiveness of sunscreen ingredients in a novel nano-surface skin cell mimic

Photophysical properties of sunscreens are commonly studied in solvent media, which do not mimic the skin, or in complex artificial skin systems, which are difficult to handle. In an earlier study, we showed that polystyrene nanosphere suspensions mimic the mixed polarity environment of skin cell systems. This paper presents a new method to quantify the effectiveness of sunscreens in the polystyrene nanosphere environment. This method utilizes the intrinsic UV-B fluorescence of polystyrene nanospheres. We studied three UV-B sunscreens by this new method and compared their extinction coefficients with observed values in solvent. The values follow the trend observed in solvents, but the ratio of their extinction coefficient in solvent to the value obtained by this new method is 1.3-1.8 instead of 1. This difference might be caused by the mixed polarity or the microgeometry of the nanosphere system. Regardless of the difference in the extinction coefficients, this new system can be used to test hundreds of chemicals for their sunscreening potential in a cost-effective way. One marked advantage of this new method is its ability to test both hydrophobic and hydrophilic sunscreening chemicals in the same environment. This is virtually impossible for current solvent-based models, which require different solvents for hydrophobic and hydrophilic chemicals. The new method also allows the simultaneous evaluation of a host of photophysical properties of sunscreening chemicals.

Photostability of commercial sunscreens upon sun exposure and irradiation by ultraviolet lamps

Background

Sunscreens are being widely used to reduce exposure to harmful ultraviolet (UV) radiation. The fact that some sunscreens are photounstable has been known for many years. Since the UV-absorbing ingredients of sunscreens may be photounstable, especially in the long wavelength region, it is of great interest to determine their degradation during exposure to UV radiation. Our aim was to investigate the photostability of seven commercial sunscreen products after natural UV exposure (UVnat) and artificial UV exposure (UVart).

Methods

Seven commercial sunscreens were studied with absorption spectroscopy. Sunscreen product, 0.5 mg/cm², was placed between plates of silica. The area under the curve (AUC) in the spectrum was calculated for UVA (320–400 nm), UVA1 (340–400 nm), UVA2 (320–340 nm) and UVB (290–320 nm) before (AUC_before) and after (AUC_after) UVart (980 kJ/m² UVA and 12 kJ/m² of UVB) and before and after UVnat. If theAUC Index (AUCI), defined as AUCI = AUC_after/AUC_before, was > 0.80, the sunscreen was considered photostable.

Results

Three sunscreens were unstable after 90 min of UVnat; in the UVA range the AUCI was between 0.41 and 0.76. In the UVB range one of these sunscreens was unstable with an AUCI of 0.75 after 90 min. Three sunscreens were photostable after 120 min of UVnat; in the UVA range the AUCI was between 0.85 and 0.99 and in the UVB range between 0.92 and 1.0. One sunscreen showed in the UVA range an AUCI of 0.87 after UVnat but an AUCI of 0.72 after UVart. Five of the sunscreens were stable in the UVB region.

Conclusion

The present study shows that several sunscreens are photounstable in the UVA range after UVnat and UVart. There is a need for a standardized method to measure photostability, and the photostability should be marked on the sunscreen product.

New strategies of photoprotection

Adequate photoprotection is essential to control UV-related disorders, including sunburn, photoaging and photocarcinogenisis. Sun avoidance, protection of skin with clothing, and sunscreens are presently the best way of photoprotection, assuming that they are used properly. However, new strategies, which are based on or make use of the endogenous protective response to UV light, may further improve currently used photoprotective means. The addition of repair enzymes and/or antioxidants has a positive effect on skin's recovery from UV-induced DNA-damage. Several botanical agents, mainly vitamins and polyphenols, have shown to influence signal transduction pathways leading to photoprotective effects. Also stimulation of endogenous UV-response pathways via irradiation with a low UV dose or via simulation of UV-induced DNA-damage results in photoprotective effects. Future research in this field and combination of different photoprotective strategies will hopefully lead to improved photoprotection.

Complexation of the sunscreen agent, 4-methylbenzylidene camphor with cyclodextrins: effect on photostability and human stratum corneum penetration

The interaction between the sunscreen agent, 4-methylbenzylidene camphor (4-MBC) and hydrophilic alpha-, beta- and gamma-cyclodextrin derivatives was investigated in water by phase-solubility analysis. Among the studied cyclodextrins, random methyl-beta-cyclodextrin (RM-beta-CD) had the greatest solubilizing activity. The complexation of the sunscreen agent with RM-beta-CD was confirmed by nuclear magnetic resonance spectroscopy and powder X-ray diffractometry. The light-induced decomposition of 4-MBC in emulsion vehicles was markedly decreased by complexation with RM-beta-CD (the extent of degradation, determined by HPLC, was 7.1% for the complex compared to 21.1% for free 4-MBC). The influence of RM-beta-CD on the human skin penetration of the sunscreen was investigated in vivo using the tape stripping method, a useful procedure for selectively removing the outermost cutaneous layers. Considerable quantities (21.2-25.1% of the applied dose) of 4-MBC permeated in the stratum corneum. However, no significant differences in the amounts of UV filter in the 10 first strips of the horny layer were observed between the formulations containing 4-MBC free or complexed with RM-beta-CD. Therefore, RM-beta-CD complexation did not alter the retention of 4-MBC in the superficial layers of the stratum corneum, where its action is more desirable.