Characterization of DNA damage inflicted by free radicals from a mutagenic sunscreen ingredient and its location using an in vitro genetic reversion assay

Trends in environmental and toxicity research on organic ultraviolet filters: A scientometric review

In recent decades, the potential toxicological and environmental effects of organic ultraviolet filters (OUVF) have received growing attention. The number of studies in this area has increased; however, presently there is no scientometric perspective addressing this topic. The purpose of this study is to identify the intellectual base and research front using the visualization and analysis software, CiteSpace. We retrieved 453 articles, published in print or online as an early-access article between 2002 and 2020, from the Web of Science with a topic search related to OUVFs, environment, and toxicology. We then analysed synthesized networks of co-authorship (author, institution, country), co-citation (author, document, journal) and co-occurring keywords. The annual publication output has trended upwards since 2002. Authors based in China accounted for 29.4% of the total publications, followed by USA (17.4%); but overall publications from Switzerland and Spain were more influential. Major research themes identified included OUVF concentrations in aquatic environments, and hormonal effects. Emerging themes included improving the sensitivity of analytical detection methods for both OUVFs and their metabolites, consequences of OUVF transport to the marine environment, and concerns over prenatal exposure. Based on keyword analysis, benzophenone-3, 4-methylbenzylidene-camphor, 3-benzylidene camphor, and ethylhexyl-methoxycinnamate are the most studied OUVFs, and effects on estrogenic activity, gene expression, reproduction, and more recently, oxidative stress, have received most attention from a toxicological perspective. Other prominent topics were sources of environmental contamination and ecological risk assessments. This study maps the major research domains of OUVF environmental toxicology research; explanations and implications of the findings are discussed; and emerging trends highlighted.

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.

Are Titania Photocatalysts and Titanium Implants Safe? Review on the Toxicity of Titanium Compounds

Titanium and its compounds are broadly used in both industrial and domestic products, including jet engines, missiles, prostheses, implants, pigments, cosmetics, food, and photocatalysts for environmental purification and solar energy conversion. Although titanium/titania-containing materials are usually safe for human, animals and environment, increasing concerns on their negative impacts have been postulated. Accordingly, this review covers current knowledge on the toxicity of titania and titanium, in which the behaviour, bioavailability, mechanisms of action, and environmental impacts have been discussed in detail, considering both light and dark conditions. Consequently, the following conclusions have been drawn: (i) titania photocatalysts rarely cause health and environmental problems; (ii) despite the lack of proof, the possible carcinogenicity of titania powders to humans is considered by some authorities; (iii) titanium alloys, commonly applied as implant materials, possess a relatively low health risk; (iv) titania microparticles are less toxic than nanoparticles, independent of the means of exposure; (v) excessive accumulation of titanium in the environment cannot be ignored; (vi) titanium/titania-containing products should be clearly marked with health warning labels, especially for pregnant women and young children; (vi) a key knowledge gap is the lack of comprehensive data about the environmental content and the influence of titania/titanium on biodiversity and the ecological functioning of terrestrial and aquatic ecosystems.

Organic ultraviolet filters in nearshore waters and in the invasive lionfish (Pterois volitans) in Grenada, West Indies

Sunscreens and other personal care products use organic ultraviolet (UV) filters such as oxybenzone, 4-methylbenzylidene camphor, Padimate-O, and octyl methoxycinnamate to prevent damage to human skin. While these compounds are effective at preventing sunburn, they have a demonstrated negative effect on cells and tissues across taxonomic levels. These compounds have a relatively short half-life in seawater but are continuously re-introduced via recreational activities and wastewater discharge, making them environmentally persistent. Because of this, testing seawater samples for the presence of these compounds may not be reflective of their abundance in the environment. Bioaccumulation of organic ultraviolet filters in a high-trophic level predator may provide greater insight to the presence and persistence of these compounds. To address this, the present study collected seawater samples as well as muscle and stomach content samples from the invasive Pacific lionfish (Pterois volitans) in the nearshore waters of Grenada, West Indies to examine the use of lionfish as potential bioindicator species. Seawater and lionfish samples were collected at four sites that are near point sources of wastewater discharge and that receive a high number of visitors each year. Samples were tested for the presence and concentrations of oxybenzone, 4-methylbenzylidene camphor (4-MBC), Padimate-O, and octyl methoxycinnamate (OMC) using liquid chromatography-mass spectrometry. Oxybenzone residues were detected in 60% of seawater samples and OMC residues were detected in 20% of seawater samples. Seawater samples collected in the surface waters near Grenada's main beach had oxybenzone concentrations more than ten times higher than seawater samples collected in less frequently visited areas and the highest prevalence of UV filters in lionfish. Residues of oxybenzone were detected in 35% of lionfish muscle and 4-MBC residues were detected in 12% of lionfish muscle. Padimate-O was not detected in either seawater or lionfish samples. No organic UV filters were detected in lionfish stomach contents. Histopathologic examination of lionfish demonstrated no significant findings attributed to UV filter toxicity. These findings report UV filter residue levels for the first time in inshore waters in Grenada. Results indicate that lionfish may be bioaccumulating residues and may be a useful sentinel model for monitoring organic ultraviolet filters in the Caribbean Sea.

Photoprotection or photodamage: a direct observation of nonradiative dynamics from 2-ethylhexyl 4-dimethylaminobenzoate sunscreen agent

Apart from being an analogue of the prototype for photoinduced intramolecular charge transfer (ICT), 2-ethylhexyl 4-dimethylaminobenzoate (EHDMABA) is also one of the earliest patented and most commonly used sunscreen components. There is, however, little documented information about the photophysics and factors affecting the photophysics of this molecule. Such information is of importance for both the understanding of the ICT reaction and assessing the underlying process of photoprotection, especially in view of the "sunscreen controversy" that has arisen from the contrasting in vivo vs. in vitro photobiological results on this and related UV filters. We report herein a femtosecond broadband time-resolved fluorescence (fs-TRF), complemented by transient absorption (fs-TA) to allow a full probe of the excited state cascades for EHDMABA and two of its derivatives in solvents of varied properties. The results provide direct evidence for a nearly solvent independent inner sphere ICT reaction occurring on the sub-picosecond time scale, and an ensuing solvent dictated deactivation of the ICT state. The ICT state in the aprotic solvent acetonitrile decayed solely through the intrinsic intersystem crossing (ISC) to produce a potentially harmful triplet excited state. In the protic solvent, the solvation and formation of ICT-induced solute-solvent hydrogen (H)-bonding opened the originally inaccessible internal conversion (IC) channel of the ICT state, leading to the rapid reformation of the ground state molecule with a unitary efficiency in the aqueous solution. This H-bonding-mediated IC restrained or eliminated the intrinsic ISC, providing a mechanism at the molecular level for the benign dissipation of the electronic excitation. The precise rate of IC was observed to vary with the alkoxy substituent and its efficiency was affected by the H-bonding capacity of the solvent. The findings of this work demonstrate the pivotal role of the microenvironment and the direct participation of solvent molecules through H-bonding in drastically altering the nonradiative dynamics and promoting or inhibiting photostability and photoprotection. This may assist in developing next-generation UV filters and help in improving formulation design for the optimal efficacy of sunscreen products. The pronounced H-bonding-induced fluorescence quenching and variation in the fluorescence wavelength imply that these molecules may also serve as a sensitive fluorescence probe for the H-bonding properties of the microenvironment.

Photophysical and photosensitizing characters of 2-phenylbenzimidazole-5-sulfonic acid. A theoretical study

The sunscreen agent 2-phenylbenzimidazole-5-sulfonic acid (PBSA) has been reported to exhibit photosensitizing activity. In the present study, the photophysical and photosensitizing properties of PBSA were investigated by means of quantum chemical calculations with the aim to gain deeper insights into the underlying photosensitizing mechanisms. The results indicate that singlet oxygen may be generated spontaneously through direct energy transfer from triplet excited state PBSA to (3)O2, and superoxide anion radical is formed through electron transfer between the anion of PBSA and (3)O2. This offers some deeper insights into the photosensitizing mechanisms of PBSA.

The quenching effect of chitosan crosslinking on ZnO nanoparticles photocatalytic activity

We report the synthesis of a non-toxic and antibacterial chitosan–ZnO composite with UV-blocking properties and efficiently quenched photocatalytic activity towards radical generation.

Nanoparticles: their potential toxicity, waste and environmental management

This literature review discusses specific issues related to handling of waste containing nanomaterials. The aims are (1) to highlight problems related to uncontrolled release of nanoparticles to the environment through waste disposal, and (2) to introduce the topics of nanowaste and nanotoxicology to the waste management community. Many nanoparticles used by industry contain heavy metals, thus toxicity and bioaccumulation of heavy metals contained in nanoparticles may become important environmental issues. Although bioavailability of heavy metals contained in nanoparticles can be lower than those present in soluble form, the toxicity resulting from their intrinsic nature (e.g. their size, shape or density) may be significant. An approach to the treatment of nanowaste requires understanding of all its properties--not only chemical, but also physical and biological. Progress in nanowaste management also requires studies of the environmental impact of the new materials. The authors believe Amara's law is applicable to the impact of nanotechnologies, and society might overestimate the short-term effects of these technologies, while underestimating the long-term effects. It is necessary to have basic information from companies about the level and nature of nanomaterials produced or emitted and about the expectation of the life cycle time of nanoproducts as a basis to estimate the level of nanowaste in the future. Without knowing how companies plan to use and store recycled and nonrecycled nanomaterials, development of regulations is difficult. Tagging of nanoproducts is proposed as a means to facilitate separation and recovery of nanomaterials.

Photoprotection

Sun exposure is the main cause of photocarcinogenesis, photoageing, and photosensitivity; thus, photoprotection is an important issue. In a skin cancer prevention strategy, behavioural measures--eg, wearing sun protective clothes and a hat and reducing sun exposure to a minimum--should be preferred to sunscreens. Often this solution is deemed to be unacceptable in our global, outdoor society, and sunscreens could become the predominant mode of sun protection for various societal reasons (eg, healthiness of a tan, relaxation in the sun). The application of a liberal quantity of sunscreen has been shown to be by far the most important factor for effectiveness of the sunscreen, followed by the uniformity of application and the specific absorption spectrum of the agent used. The sunscreen market--crowded by numerous products--shows various differences worldwide. Nevertheless, sunscreens should not be abused in an attempt to increase time in the sun to a maximum. Controversies about safety of sunscreens and clinical recommendations are discussed.

Xenoestrogens modulate genotoxic (UVB)-induced cellular responses in estrogen receptors positive human breast cancer cells

Human populations and wildlife are exposed to mixtures of both anthropogenic and natural chemicals. Some of these compounds are known to interact principally with the endocrine function, whereas others act mainly on genomic DNA. Given this evidence, we wanted to address the question of whether concomitant exposure of such chemicals was able to interact at the cellular level. We have previously shown that 17β-Estradiol (E(2)) modulates the DNA repair capacity of cells. In this work, we wanted to examine if other xenoestrogens (i.e. industrial compounds, pesticides or pharmaceuticals) were able to interact with the UVB-induced cellular response as E(2) does. Here, we show that xenoestrogens modulate the capacity of cells to repair their DNA damage according to the type of compounds. For example, the oral contraceptive 17α-Ethinylestradiol down-regulated the repair of UVB-induced DNA damage whereas the UV filter Eusolex 6007 up-regulated this pathway. The notion that xenoestrogens could interact with a genotoxic stress is reinforced by the modulation of the estrogens-dependent luciferase reporter gene expression when cells are UVB-irradiated. Finally, these observations suggested the potential role of xenoestrogens in carcinogenesis by their capacity to modulate cells responses to genotoxic stress.

Human Safety and Efficacy of Ultraviolet Filters and Sunscreen Products

Ultraviolet (UV) filters are the active ingredients in sunscreens. The concentration and combination of UV filters determine the efficacy of sunscreens as measured by sun protection factor. The safety of individual UV filters, and, more generally, sunscreen products, is a matter of a few related components: objective toxicologic evaluation, phototoxicologic potential, and human health consequences of using products that may reduce some but not all of the solar UV. Of 16 UV filters approved by the US Food and Drug Administration, 9 are used in different combinations in the most currently marketed sunscreens. Most of these compounds are considered safe and effective alone or in combination with other UV filters based on extensive toxicologic/phototoxicologic evaluations and market history. The benefits from proper use of sunscreens outweigh real or perceived human health concerns, establishing a favorable benefit-to-risk ratio. Future UV filters will require complete human safety evaluations alone and in combination with select benchmark ingredients.

Reactive oxygen species produced upon photoexcitation of sunscreens containing titanium dioxide (an EPR study)

Commercial sunscreen products containing titanium dioxide were irradiated with lambda>300 nm and the formation of oxygen- (.OH, O2.-/.OOH) and carbon-centered radicals was monitored by EPR spectroscopy and spin trapping technique using 5,5-dimethyl-1-pyrroline N-oxide, alpha-phenyl-N-tert-butylnitrone (PBN), alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone as spin traps, and free nitroxide radical 4-hydroxy-2,2,6,6-tetramethylpiperidine N-oxyl. The photoinduced production of singlet oxygen was shown by 4-hydroxy-2,2,6,6-piperidine. The generation of reactive oxygen radical species upon irradiation of sunscreens significantly depends on their composition, as the additives present (antioxidants, radical-scavengers, solvents) can transform the reactive radicals formed to less harmful products. The continuous in situ irradiation of titanium dioxide powder, recommended for cosmetic application, investigated in different solvents (water, dimethyl sulfoxide, isopropyl myristate) resulted in the generation of oxygen-centered reactive radical species (superoxide anion radical, hydroxyl and alkoxyl radicals).

Ultraviolet protective performance of photoprotective lipsticks: change of spectral transmittance because of ultraviolet exposure

BACKGROUND

Photoinstability of sunscreens because of ultraviolet (UV) exposure is a well-known and common phenomenon. Recently, it was also shown that sunscreens with complex filter combinations are photoinactivated by UV exposures, which can easily be acquired by solar exposure over several hours.

OBJECTIVES

To assess the change of the spectral transmission after UV exposure (UV-challenged protective performance) of 27 commercially available photoprotective lipsticks.

METHODS

Quartz slides were covered with a lipstick layer (area density 1.0+/-0.1 mg/cm2) and irradiated with increasing doses of solar-simulated radiation. The spectral transmission (T) was measured spectrophotometrically before and after 5, 12.5, 25, and 50 standard erythema doses (SED) of exposure. We calculated the change in transmission (photoinstability) as the difference between the spectral transmission before and after a defined UV exposure, DeltaT, and the arithmetic mean, for both the UVA (DeltaTA) and UVB (DeltaTB) ranges. A product was labelled as photounstable if the mean photoinstability in the UVA, DeltaTA, or UVB range, DeltaTB, was higher than 5% for an UV exposure of 12.5 SED.

RESULTS

Eleven products showed a significant photoinstability in the UVA range (DeltaTA between 6% and 27%), only one product in the UVB range (DeltaTB = 13%), and one product in both the UVA (DeltaTA = 31%) and UVB (DeltaTB = 9%) range. In one product photoinstability became significant in the UVA range at higher UV exposures.

CONCLUSIONS

Out of 27 lipsticks only 13 products showed a photostable performance (DeltaTA < 5% and DeltaTB < 5% for 12.5 SED). We propose therefore that only products, which fulfil these UV photostability criteria should be marketed.

Optical spectroscopy of hydrophobic sunscreen molecules adsorbed to dielectric nanospheres

Fluorescence and absorption spectra of hydrophobic sunscreens, weakly fluorescent octyl methoxycinnamate, moderately fluorescent octyl salicylate and highly fluorescent 2-ethylhexyl-4-(dimethylamino)benzoate (padimate O) adsorbed to dielectric microspheres in aqueous suspension, have been compared with spectra in organic solution. The fluorescence of adsorbed salicylate and padimate is enhanced compared with fluorescence in methanol: about a factor of 6 and 30 in terms of fluorescence yield per molecule of salicylate and padimate, respectively. Cinnamate, which has a low fluorescence yield, does not show a comparable fluorescence enhancement. The fluorescence amplification is independent of sphere diameter from 30 to 1500 nm, at least for salicylate. The enhancement, as well as the location of absorption spectral peaks, is consistent with a low-dielectric constant environment of the molecules, in spite of the presumed location near the interface between polystyrene (epsilon = 2.4-3.8) and water (epsilon = 78). The adsorbed state of these sunscreens represents a proposed improved in vitro model for the environment of sunscreens in vivo, as well as a general model for chromophores in heterogeneous environments.

An in vitro systematic spectroscopic examination of the photostabilities of a random set of commercial sunscreen lotions and their chemical UVB/UVA active agents

The photostabilities of a random set of commercially available sunscreen lotions and their active ingredients are examined spectroscopically subsequent to simulated sunlight UV exposure. Loss of filtering efficacy can occur because of possible photochemical modifications of the sunscreen active agents. Changes in absorption of UVA/ UVB sunlight by agents in sunscreen lotions also leads to a reduction of the expected photoprotection of human skin and DNA against the harmful UV radiation. The active ingredients were investigated in aqueous media and in organic solvents of various polarities (methanol, acetonitrile, and n-hexane) under aerobic and anaerobic conditions The UV absorption features are affected by the nature of the solvents with properties closely related to oil-in-water (o/w) or water-in-oil (w/o) emulsions actually used in sunscreen formulations, and by the presence of molecular oxygen. The photostabilities of two combined chemical ingredients (oxybenzone and octyl methoxycinnamate) and the combination oxybenzone/titanium dioxide were also explored. In the latter case, oxybenzone undergoes significant photodegradation in the presence of the physical filter TiO2.

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

Regarding the outdoor behavior of the Caucasian population, modern sunscreens should provide high and broad-spectrum ultraviolet protection in the ultraviolet B as well as in the ultraviolet A range and should be photochemically stable for ultraviolet doses, which can be expected in solar radiation. At present an assessment of the photostability of suncare products is not a general requirement before marketing. In order to evaluate the photostability of suncare products we conducted an in vitro test and measured the spectral absorbance of 16 sunscreens before, and after exposure to increasing biologically weighted standard erythema doses (5, 12.5, 25, 50) of solar-simulated radiation. Seven of 16 suncare products showed a significant dose- and wavelength-dependent decrease of the ultraviolet A protective capacity, whereas the ability to absorb ultraviolet B was not affected. In the ultraviolet A range, the decrease of absorbance (photoinactivation), respectively, the increase of transmission was 12-48% for an ultraviolet exposure of 25 standard erythema dose. Photoinactivation started in the wavelength range between 320 and 335 nm with a maximum above 350 nm. Furthermore, our analysis showed that the behavior of suncare products was not predictable from its individual ingredients. Neither complex combinations of organic filters nor addition of inorganic filters could absolutely prevent photoinactivation. The inclusion of a single photounstable filter did not mean photoinstability of the complete suncare product. Photoinactivation of sunscreens appears to be an underestimated hazard to the skin, first, by formation of free radicals, second, by increased ultraviolet A transmission.

Photosensitization of the sunscreen octyl p-dimethylaminobenzoate by UVA in human melanocytes but not in keratinocytes

Sunscreens penetrate human epidermis and modify the biology of proliferating cells. This study addressed the question whether the UV response of cultured human cells is affected by direct treatment with nontoxic levels of sunscreens. Cell survival following exposure to UVC or unfiltered UBV was not altered by preincubation with 25 micrograms/mL of octyl p-dimethylaminobenzoate (o-PABA), 2-ethylhexyl p-methoxycinnamate (EHMC) or oxybenzone. However, UVA or UVB filtered to reproduce the solar UV spectrum penetrating to the basal layer of the epidermis, highly sensitized cells to killing by o-PABA but not by its hydrolysis product, 4-dimethylaminobenzoic acid. Sensitization was found in all cell types tested, except normal keratinocytes, and could be prevented by certain antioxidants particularly pyruvate and the hydroxyl radical scavenger mannitol. o-PABA and EHMC applied without UV reduced the adherence of cells. The results indicate that sunscreens may increase cell mobility and the combination of o-PABA with solar UV may selectively damage melanocytes in the skin.

Illumination of human keratinocytes in the presence of the sunscreen ingredient Padimate-O and through an SPF-15 sunscreen reduces direct photodamage to DNA but increases strand breaks

On illumination with simulated sunlight, the UVB-absorbing sunscreen chemical 2-ethylhexyl-4-dimethylaminobenzoate (Padimate-O) generates excited species which inflict non-ligatable strand breaks on DNA in vitro and it also becomes mutagenic to yeast in vivo. Padimate-O is known to penetrate human skin but its effects on human cells are not clear. Here, we first simulate the sunlight which penetrates human skin and use it to illuminate human keratinocytes. The DNA damage observed in terms of UV-endonuclease-sensitive sites (ESS) and direct strand breaks per kilobase (kb) of DNA per joule per square metre agrees well with that predicted from action spectra based on monochromatic light. Using plasmid DNA in vitro, we find a very similar pattern of results. Next, we simulate the spectrum that results when the incident light is first attenuated by a film of sunscreen (SPF-15; 2 mg/cm(2)) containing benzophenone-3 (a UVA absorber), octyl methoxycinnamate (a UVB absorber), and Padimate-O. If the sunscreen is not in contact with keratinocytes it reduces direct DNA damage from sunlight (ESS). However, any Padimate-O in contact with the cells substantially increases indirect damage (strand breaks) even though the film of sunscreen reduces direct photodamage. We estimate that applying an SPF-15 sunscreen which contains Padimate-O to human skin followed by exposure to only 5 minimum erythemal doses (MED) of sunlight could, while suppressing the formation of ESS, increase strand breaks in cells under the epidermis by at least 75-fold compared to exposure to 1 MED in the absence of sunscreen.

Nitroxide radicals protect DNA from damage when illuminated in vitro in the presence of dibenzoylmethane and a common sunscreen ingredient

Indolinonic nitroxide radicals efficiently scavenge oxygen- and carbon-centered radicals. They protect lipid and protein systems against oxidative stress, but little is known about their capacity to protect DNA against radical-mediated damage. We compare indolinonic nitroxides and the piperidines TEMPO and TEMPOL for their ability to inhibit strand breaks inflicted on DNA when it is illuminated in vitro in the presence of dibenzoylmethane (DBM) and a relative, Parsol 1789, used as a UVA-absorbing sunscreen. We used spin-trapping EPR to examine the formation of radicals and plasmid nicking assays to evaluate DNA strand breakage. The results have a two-fold interest. First, they show that all the nitroxides tested efficiently prevent DNA damage in a dose-dependent fashion. Vitamin E had no effect under the conditions used. Second, they show that carbon-centered radicals are produced on illumination of DBM and its relative and that their formation is probably responsible for the direct strand breaks found when naked DNA is illuminated in vitro in their presence. Additional work on the ability of sunscreens to enter human cells and their response to the light that penetrates sunscreen-protected skin would be necessary before any conclusion could be drawn as to whether the results reported here are relevant to human use of sunscreens.

Chemical oxidation and DNA damage catalysed by inorganic sunscreen ingredients

Titanium dioxide (TiO2) has been noted (US Federal Register, 43FR38206, 25 August 1978) to be a safe physical sunscreen because it reflects and scatters UVB and UVA in sunlight. However, TiO2 absorbs about 70% of incident UV, and in aqueous environments this leads to the generation of hydroxyl radicals which can initiate oxidations. Using chemical methods, we show that all sunscreen TiO2 samples tested catalyse the photo-oxidation of a representative organic substrate (phenol). We also show that sunlight-illuminated TiO2 catalyses DNA damage both in vitro and in human cells. These results may be relevant to the overall effects of sunscreens.