A Sunscreen's Labeled Sun Protection Factor May Overestimate Protection at Temperate Latitudes: A Human In Vivo Study

Comparison of photodamage in non-pigmented and pigmented human skin equivalents exposed to repeated ultraviolet radiation to investigate the role of melanocytes in skin photoprotection

Introduction

Daily solar ultraviolet (UV) radiation has an important impact on skin health. Understanding the initial events of the UV-induced response is critical to prevent deleterious conditions. However, studies in human volunteers have ethical, technical, and economic implications that make skin equivalents a valuable platform to investigate mechanisms related to UV exposure to the skin. In vitro human skin equivalents can recreate the structure and function of in vivo human skin and represent a valuable tool for academic and industrial applications. Previous studies have utilised non-pigmented full-thickness or pigmented epidermal skin equivalents to investigate skin responses to UV exposure. However, these do not recapitulate the dermal-epidermal crosstalk and the melanocyte role in photoprotection that occurs in vivo. In addition, the UV radiation used in these studies is generally not physiologically representative of real-world UV exposure.

Methods

Well-characterised pigmented and non-pigmented skin equivalents that contain human dermal fibroblasts, endogenous secreted extracellular matrix proteins (ECM) and a well-differentiated and stratified epidermis have been developed. These constructs were exposed to UV radiation for ×5 consecutive days with a physiologically relevant UV dose and subsequently analysed using appropriate end-points to ascertain photodamage to the skin.

Results

We have described that repeated irradiation of full-thickness human skin equivalents in a controlled laboratory environment can recreate UV-associated responses in vitro, mirroring those found in photoexposed native human skin: morphological damage, tanning, alterations in epidermal apoptosis, DNA lesions, proliferation, inflammatory response, and ECM-remodelling.

Discussion

We have found a differential response when using the same UV doses in non-pigmented and pigmented full-thickness skin equivalents, emphasising the role of melanocytes in photoprotection.

The adverse consequences of not using sunscreens

The adverse effects of solar ultraviolet radiation (UVR) on normal skin are well established, especially in those with poorly melanized skin. Clinically, these effects may be classified as acute, such as erythema or chronic such as keratinocyte and melanocyte skin cancers. Apart from skin type genetics, clinical responses to solar UVR are dependent on geophysical (e.g., solar intensity) and behavioural factors. The latter are especially important because they may result in 'solar overload' with unwanted clinical consequences and ever greater burdens to healthcare systems. Correctly used, sunscreens can mitigate the acute and chronic effects of solar UVR exposure. Laboratory studies also show that sunscreens can inhibit the initial molecular and cellular events that are responsible for clinical outcomes. Despite public health campaigns, global trends continue to show increasing incidence of all types of skin cancer. Large-scale epidemiological studies have shown the benefits of sunscreen use in preventing skin cancer, though it is likely that sunscreen use has not been optimal in such studies. It is evident that without substantial changes in sun-seeking behaviour, sunscreen use is a very important part of the defence against the acute and chronic effects of solar exposure. Ideally, sunscreens should be able to provide the level of protection that reduces the risk of skin cancer in susceptible skin types to that observed in heavily melanized skin.

Review on photoprotection: a clinician’s guide to the ingredients, characteristics, adverse effects, and disease-specific benefits of chemical and physical sunscreen compounds

Photoprotection is a critical health prevention strategy to reduce the deleterious effects of ultraviolet radiation (UVR) and visible light (VL). Methods of photoprotection are reviewed in this paper, with an emphasis on sunscreen. The most appropriate sunscreen formulation for personal use depends on several factors. Active sunscreen ingredients vary in their protective effect over the UVR and VL spectrum. There are dermatologic diseases that cause photosensitivity or that are aggravated by a particular action spectrum. In these situations, sunscreen suggestions can address the specific concern. Sunscreen does not represent a single entity. Appropriate personalized sunscreen selection is critical to improve compliance and clinical outcomes. Health care providers can facilitate informed product selection with awareness of evolving sunscreen formulations and counseling patients on appropriate use. This review aims to summarize different forms of photoprotection, discuss absorption of sunscreen ingredients, possible adverse effects, and disease-specific preferences for chemical, physical or oral agents that may decrease UVR and VL harmful effects.

Perspectives on Cyclobutane Pyrimidine Dimers-Rise of the Dark Dimers†

Some early reports demonstrate that levels of cyclobutane pyrimidine dimers (CPD) may increase after UVR exposure had ended, although these observations were treated as artifacts. More recently, it has been shown unequivocally that CPD formation does occur post-irradiation, with maximal levels occurring after about 2-3 h. These lesions have been termed "dark CPD" (dCPD). Subsequent studies have confirmed their presence in vitro, in mouse models and in human skin in vivo. Melanin carbonyls have a role in the formation of dCPD, but they have also been observed in amelanotic systems, indicating other, unknown process(es) exist. In both cases, the formation of dCPD can be prevented by the presence of certain antioxidants. We lack data on the spectral dependence of dCPD, but it is unlikely to be the same as for incident CPD (iCPD), which are formed only during irradiation. There is evidence that iCPD and dCPD may have different repair kinetics, although this remains to be elucidated. It is also unknown whether iCPD and dCPD have different biological properties. The formation of dCPD in human skin in vivo has implications for post solar exposure photoprotection, and skin carcinogenesis, with a need for this to be investigated further.

Sunscreen photoprotection and vitamin D status

Background

Global concern about vitamin D deficiency has fuelled debates on photoprotection and the importance of solar exposure to meet vitamin D requirements.

Objectives

To review the published evidence to reach a consensus on the influence of photoprotection by sunscreens on vitamin D status, considering other relevant factors.

Methods

An international panel of 13 experts in endocrinology, dermatology, photobiology, epidemiology and biological anthropology reviewed the literature prior to a 1‐day meeting in June 2017, during which the evidence was discussed. Methods of assessment and determining factors of vitamin D status, and public health perspectives were examined and consequences of sun exposure and the effects of photoprotection were assessed.

Results

A serum level of ≥ 50 nmol L⁻¹ 25(OH)D is a target for all individuals. Broad‐spectrum sunscreens that prevent erythema are unlikely to compromise vitamin D status in healthy populations. Vitamin D screening should be restricted to those at risk of hypovitaminosis, such as patients with photosensitivity disorders, who require rigorous photoprotection. Screening and supplementation are advised for this group.

Conclusions

Sunscreen use for daily and recreational photoprotection does not compromise vitamin D synthesis, even when applied under optimal conditions.

What's already known about this topic?

Knowledge of the relationship between solar exposure behaviour, sunscreen use and vitamin D is important for public health but there is confusion about optimal vitamin D status and the safest way to achieve this.

Practical recommendations on the potential impact of daily and/or recreational sunscreens on vitamin D status are lacking for healthy people.

What does this study add?

Judicious use of daily broad‐spectrum sunscreens with high ultraviolet (UV) A protection will not compromise vitamin D status in healthy people.

However, photoprotection strategies for patients with photosensitivity disorders that include high sun‐protection factor sunscreens with high UVA protection, along with protective clothing and shade‐seeking behaviour are likely to compromise vitamin D status.

Screening for vitamin D status and supplementation are recommended in patients with photosensitivity disorders.

Linked Comment: https://doi.org/10.1111/bjd.18126.

https://doi.org/10.1111/bjd.18494 available online

Optimal sunscreen use, during a sun holiday with a very high ultraviolet index, allows vitamin D synthesis without sunburn

Background

Sunlight contains ultraviolet (UV)A and UVB radiation. UVB is essential for vitamin D synthesis but is the main cause of sunburn and skin cancer. Sunscreen use is advocated to reduce the sun's adverse effects but may compromise vitamin D status.

Objectives

To assess the ability of two intervention sunscreens to inhibit vitamin D synthesis during a week‐long sun holiday.

Methods

The impact of sunscreens on vitamin D status was studied during a 1‐week sun holiday in Tenerife (28° N). Comparisons were made between two formulations, each with a sun protection factor (SPF) of 15. The UVA‐protection factor (PF) was low in one case and high in the other. Healthy Polish volunteers (n = 20 per group) were given the sunscreens and advised on the correct application. Comparisons were also made with discretionary sunscreen use (n = 22) and nonholiday groups (51·8° N, n = 17). Sunscreen use in the intervention groups was measured. Behaviour, UV radiation exposure, clothing cover and sunburn were monitored. Serum 25‐hydroxyvitamin D₃ [25(OH)D₃] was assessed by high‐performance liquid chromatography–tandem mass spectrometry.

Results

Use of intervention sunscreens was the same (P = 0·60), and both equally inhibited sunburn, which was present in the discretionary use group. There was an increase (P < 0·001) in mean ± SD 25(OH)D₃ (28·0 ± 16·5 nmol L⁻¹) in the discretionary use group. The high and low UVA‐PF sunscreen groups showed statistically significant increases (P < 0·001) of 19·0 ± 14·2 and 13·0 ± 11·4 nmol L⁻¹ 25(OH)D₃, respectively with P = 0·022 for difference between the intervention sunscreens. The nonholiday group showed a fall (P = 0·08) of 2·5 ± 5·6 nmol L⁻¹ 25(OH)D₃.

Conclusions

Sunscreens may be used to prevent sunburn yet allow vitamin D synthesis. A high UVA‐PF sunscreen enables significantly higher vitamin D synthesis than a low UVA‐PF sunscreen because the former, by default, transmits more UVB than the latter.

What's already known about this topic?

Action spectra (wavelength dependence) for erythema and the cutaneous formation of vitamin D overlap considerably in the ultraviolet (UV)B region.

Theoretically, sunscreens that inhibit erythema should also inhibit vitamin D synthesis.

To date, studies on the inhibitory effects of sunscreens on vitamin D synthesis have given conflicting results, possibly, in part, because people typically apply sunscreen suboptimally.

Many studies have design flaws.

What does this study add?

Sunscreens (sun protection factor, SPF 15) applied at sufficient thickness to inhibit sunburn during a week‐long holiday with a very high UV index still allow a highly significant improvement of serum 25‐hydroxyvitamin D₃ concentration.

An SPF 15 formulation with high UVA protection enables better vitamin D synthesis than a low UVA protection product. The former allows more UVB transmission.

Linked Editorial: https://doi.org/10.1111/bjd.18273.

https://doi.org/10.1111/bjd.18492 available online

https://www.bjdonline.com/article/optimal-sunscreen-use-during-a-sun-holiday-with-a-very-high-ultraviolet-index-allows-vitamin-d-synthesis-without-sunburn/

Is Sunlight Exposure Enough to Avoid Wintertime Vitamin D Deficiency in United Kingdom Population Groups?

Solar ultraviolet radiation (UVR) is required for cutaneous vitamin D synthesis, and experimental studies have indicated the levels of sun exposure required to avoid a vitamin D deficient status. Our objectives are to examine the sun exposure behaviours of different United Kingdom sectors and to identify if their exposure is enough to maintain winter circulating 25-hydroxyvitamin D above deficiency (>25 nmol/L). Data are from a series of human studies involving >500 volunteers and performed using the same protocols in Greater Manchester, UK (53.5° N) in healthy white Caucasian adolescents and working-age adults (skin type I⁻IV), healthy South Asian working-age adults (skin type V), and adults with photodermatoses (skin conditions caused or aggravated by cutaneous sun exposure). Long-term monitoring of the spectral ambient UVR of the Manchester metropolitan area facilitates data interpretation. The healthy white populations are exposed to 3% ambient UVR, contrasting with ~1% in South Asians. South Asians and those with photodermatoses wear clothing exposing smaller skin surface area, and South Asians have the lowest oral vitamin D intake of all groups. Sun exposure levels prevent winter vitamin D deficiency in 95% of healthy white adults and 83% of adolescents, while 32% of the photodermatoses group and >90% of the healthy South Asians were deficient. The latter require increased oral vitamin D, whilst their sun exposure provides a tangible contribution and might convey other health benefits.

Polycomb group proteins: Novel molecules associated with ultraviolet A-induced photoaging of human skin

Epigenetic repressor polycomb group (PcG) proteins are thought to serve a role in a number of cellular processes, including carcinogenesis, senescence, apoptosis and DNA repair. In the present study, long-wave ultraviolet A (UVA) was used to irradiate human skin fibroblasts (HSFs) and embryonic skin fibroblasts (ESFs) in order to simulate photoaging of the skin. The results of cell proliferation, apoptosis, hyaluronic acid (HA) content and reverse transcription-quantitative polymerase chain reaction assays revealed that the expression levels of genes encoding key PcG proteins (BMI-1 and EZH2) were altered. In addition, the expression levels of these genes were associated with the expression of enzymes that regulate HA synthesis. Furthermore, the expression levels of PcG proteins differed between HSFs and ESFs, suggesting that PcG proteins serve a role in altering HA synthesis during the UVA-induced fibroblast aging process. This signaling pathway may represent a novel molecular mechanism regulating the photoaging of the skin. The findings of the present study provide important insights into the underlying mechanisms of photoaging of the human skin. Further studies are required to clarify the molecular mechanisms underling skin aging and to identify targets for the clinical treatment of photoaging.

Vitamin D Supplementation Does Not Improve the Severity or the Resolution of Ultraviolet B-Induced Acute Erythema

BACKGROUND

Whether vitamin D supplementation alleviates the severity of ultraviolet B (UVB)-induced erythema and/or facilitates its resolution remains undetermined.

OBJECTIVE

To study the effect of oral vitamin D on UVB-induced erythema and its resolution in fair-skinned subjects.

METHODS

UVB-induced erythema was quantified using a Chroma Meter® in 50 volunteers 48 h before and 10 days after the random administration of 200,000 IU vitamin D (n = 40) or placebo (n = 10). Resolution of erythema in both groups was assessed by chromametry 24, 48, and 72 h after vitamin D administration.

RESULTS

No statistical difference between erythema values before and after administration in the vitamin D-supplemented group (p = 0.44) or the placebo group (p = 0.34) was noted. No statistical difference was evident between both groups with respect to resolution of erythema (p = 0.30).

CONCLUSION

Oral vitamin D supplementation neither improves protection against UVB-induced erythema nor facilitates its resolution.

Exposure to non-extreme solar UV daylight: spectral characterization, effects on skin and photoprotection

The link between chronic sun exposure of human skin and harmful clinical consequences such as photo-aging and skin cancers is now indisputable. These effects are mostly due to ultraviolet (UV) rays (UVA, 320–400 nm and UVB, 280–320 nm). The UVA/UVB ratio can vary with latitude, season, hour, meteorology and ozone layer, leading to different exposure conditions. Zenithal sun exposure (for example on a beach around noon under a clear sky) can rapidly induce visible and well-characterized clinical consequences such as sunburn, predominantly induced by UVB. However, a limited part of the global population is exposed daily to such intense irradiance and until recently little attention has been paid to solar exposure that does not induce any short term clinical impact. This paper will review different studies on non-extreme daily UV exposures with: (1) the characterization and the definition of the standard UV daylight and its simulation in the laboratory; (2) description of the biological and clinical effects of such UV exposure in an in vitro reconstructed human skin model and in human skin in vivo, emphasizing the contribution of UVA rays and (3) analysis of photoprotection approaches dedicated to prevent the harmful impact of such UV exposure.

Highly sensitive biological assay for determining the photoprotective efficacy of sunscreen

The protective effect of sunscreens has been extensively evaluated in vivo as a measure of erythema induced in human skin and is expressed as Sun Protection Factor (SPF). In vitro alternatives that use human cells might overcome the limitations of testing on human beings. Here is proposed a broad and accurate in vitro approach for evaluating the efficacy of commercial sunscreens even under environmental conditions. This Cell dosimeter allowed the determination of Sun Protection Factor for DNA (DNA-SPF), using specific DNA repair enzymes and antibodies, and Sun Protection Factor for Lethal Damage (LD-SPF), by measuring cell viability and apoptosis induced after the irradiation of human cells. The use of xeroderma pigmentosum (XP) cells, which are deficient in DNA repair, rendered this assay more sensitive. The results revealed significant protection against the effects elicited by UVB radiation; however, there was no efficient protection from DNA lesions and cell death induced by UVA radiation or natural sunlight. This work demonstrates the environmental application of this biodosimeter for measuring UV-induced biological damage to human cells and supports the need for better evaluation of the UVA protection efficacy conferred by commercial sunscreens, in terms of induction of DNA lesions and cell death.

DNA damage as a biological sensor for environmental sunlight

Solar ultraviolet (UV) radiation is widely known as an environmental genotoxic agent that affects ecosystems and the human population, generating concerns and motivating worldwide scientific efforts to better understand the role of sunlight in the induction of DNA damage, cell death, mutagenesis, and ultimately, carcinogenesis. In this review, general aspects of UV radiation at the Earth's surface are reported, considering measurements by physical and biological sensors that monitor solar UV radiation under different environmental conditions. The formation of DNA photoproducts and other types of DNA damage by different UV wavelengths are compared with the present information on their roles in inducing biological effects. Moreover, the use of DNA-based biological dosimeters is presented as a feasible molecular and cellular tool that is focused on the evaluation of DNA lesions induced by natural sunlight. Clearly, direct environmental measurements demonstrate the biological impact of sunlight in different locations worldwide and reveal how this affects the DNA damage profile at different latitudes. These tools are also valuable for the quantification of photoprotection provided by commercial sunscreens against the induction of DNA damage and cell death, employing DNA repair-deficient cells that are hypersensitive to sunlight. Collectively, the data demonstrate the applicability of DNA-based biosensors as alternative, complementary, and reliable methods for registering variations in the genotoxic impact of solar UV radiation and for determining the level of photoprotection sunscreens provided at the level of DNA damage and cell death.

UVA1 is skin deep: molecular and clinical implications

Long wavelength UVA1 (340-400 nm) is the main component of terrestrial UVR and is increasingly used in skin phototherapy. Its damage to critical biomolecules such as DNA has been widely attributed to its ability to generate reactive oxygen species (ROS) via other chromophores. However recent studies in vitro and in vivo have shown that UVA1 has a specific ability to generate cyclobutane pyrimidine dimers (CPD), especially thymine dimers (T<>T), and that this is probably due to direct absorption of UVR. The CPD has been implicated in many aspects of skin cancer. Measuring UVB-induced CPD in the epidermis and dermis in vivo shows that, as expected, the skin attenuates UVB. In contrast, our data show that this is not the case with UVA1: in fact there is more damage with increased skin depth. This suggests that the basal layer, which contains keratinocyte stem cells and melanocytes, is more vulnerable to the carcinogenic effects of UVA1 than would be predicted by mouse models. These data support the continuing trend for better UVA1 protection by sunscreens.

Sunburn protection as a function of sunscreen application thickness differs between high and low SPFs

BACKGROUND

Sunscreens are an important component of healthy sun-protection behavior. To achieve satisfactory protection, sunscreens must be applied consistently, evenly and correctly. Consumers do not apply sunscreen properly and, therefore, do not achieve the protection indicated by the label 'sun protection factor' (SPF). The objective of the present study was to determine the actual sun(burn) protection given by a range of sunscreen application thickness levels for both low and high SPF formulas.

SUBJECTS AND METHODS

Forty study subjects were recruited from each of three geographical regions in China. Sunscreens with label SPFs of 4, 15, 30, and 55 were tested at application levels of 0.5, 1.0, 1.5, and 2.0 mg/cm(2) in three laboratories using a standard SPF protocol.

RESULTS

Sunscreens with lower SPFs (4 and 15) showed a linear dose-response relationship with application level, but higher SPF (30 and 55) product protection was exponentially related to application thickness.

CONCLUSION

Sunscreen protection is not related in one uniform way to the amount of product applied to human skin. Consumers may achieve an even lower than expected sunburn protection from high SPF products than from low SPF sunscreens.

DNA Dosimetry Assessment for Sunscreen Genotoxic Photoprotection

Background

Due to the increase of solar ultraviolet radiation (UV) incidence over the last few decades, the use of sunscreen has been widely adopted for skin protection. However, considering the high efficiency of sunlight-induced DNA lesions, it is critical to improve upon the current approaches that are used to evaluate protection factors. An alternative approach to evaluate the photoprotection provided by sunscreens against daily UV radiation-induced DNA damage is provided by the systematic use of a DNA dosimeter.

Methodology/Principal Findings

The Sun Protection Factor for DNA (DNA-SPF) is calculated by using specific DNA repair enzymes, and it is defined as the capacity for inhibiting the generation of cyclobutane pyrimidine dimers (CPD) and oxidised DNA bases compared with unprotected control samples. Five different commercial brands of sunscreen were initially evaluated, and further studies extended the analysis to include 17 other products representing various formulations and Sun Protection Factors (SPF). Overall, all of the commercial brands of SPF 30 sunscreens provided sufficient protection against simulated sunlight genotoxicity. In addition, this DNA biosensor was useful for rapidly screening the biological protection properties of the various sunscreen formulations.

Conclusions/Significance

The application of the DNA dosimeter is demonstrated as an alternative, complementary, and reliable method for the quantification of sunscreen photoprotection at the level of DNA damage.

Light source spectrum strongly influences the in vitro estimation of sun protection factor

Irradiation from an artificial solar simulator that matches the relative cumulative erythema effectiveness (RCEE) of sunlight is used for in vivo sun protection factor (SPF) testing, whereas irradiation that matches the spectrum of natural sunlight (NS) is generally used for in vitro SPF testing. This study was designed to clarify whether this difference is important. Eight sunscreens spread on artificial substrates and several optical filters as sunscreen mimics were used. Their in vitro SPF values were evaluated using RCEE-compliant and NS spectrum-matching light sources in calculation. The calculated in vitro SPF values obtained using NS light (SPF [NS]) were lower than those obtained using RCEE light (SPF [RCEE]). The in vitro SPF (RCEE) values showed a better correlation and better agreement with in vivo SPF values, as compared with the in vitro SPF (NS) values. A marked difference between in vitro SPF values obtained with the two light sources in calculation was found for sunscreens showing low transmittance in the ultraviolet B region. To obtain in vitro SPF values that correspond well to in vivo SPF values measured with currently accepted methodology, it is important to use an RCEE-compliant light source.

Human erythema and matrix metalloproteinase-1 mRNA induction, in vivo, share an action spectrum which suggests common chromophores

Matrix metalloproteinase 1 (MMP-1) is widely regarded as a biomarker of photoageing. We tested the hypothesis that MMP-1 mRNA expression and erythema share a common action spectrum by comparing the effects of erythemally equivalent doses of UVB, UVA1 and solar simulated radiation (SSR) on acute MMP-1 mRNA expression in whole human skin in vivo. Our results show comparable MMP-1 expression with all three spectra, which supports our hypothesis. The sharing of an action spectrum implies common chromophores, one of which is likely to be DNA. We have previously shown that all spectra that we used readily induce cyclobutane thymine dimers (T<>T) in human epidermis in vivo but we lack quantitative data on damage to dermal DNA. This is important because we do not know if dermal MMP-1 induction occurs via direct damage to the dermis, or indirectly via damage to the epidermis. Our results show that UVB induces about 3 times more T<>T compared with erythemally equivalent doses of UVA1, which is similar to our published epidermal data. This supports previously published work that also implicates an unknown UVA1 chromophore for erythema and MMP-1 induction. However, the distribution of the dermal DNA damage varies considerably with spectrum. In the case of UVB it is primarily in the upper dermis, but with UVA1 it is evenly distributed. Thus, irrespective of chromophores, MMP-1 induction by direct dermal damage by both spectra is possible. The practical conclusions of our data are that the small (<5%) UVB content of solar UVR is likely to be the main cause of photoageing, at least in terms of MMP-1 expression. Furthermore, prevention of erythema by sunscreen use is likely to result in reduced MMP-1 expression.

Topical liposomal DNA-repair enzymes in polymorphic light eruption

Polymorphic light eruption (PLE) is a very frequent photodermatosis in Europe whose pathogenesis may involve resistance to UV-induced immune suppression and simultaneous immune reactions against skin photoneoantigens. We performed a randomized, double-blind, placebo-controlled intra-individual half-body trial to investigate the protective effect of an after-sun (AS) lotion containing DNA-repair enzymes (photolyase from Anacystis nidulans and Micrococcus luteus extract with endonuclease activity). Fourteen PLE patients were exposed to suberythemal doses of solar-simulated UV radiation on 4 consecutive days at 4 symmetrically located PLE-prone test fields per patient. The test fields were treated with (i) active AS lotion or (ii) a placebo lotion immediately after each UV exposure, or (iii) an SPF30 sunscreen before UV exposure or left untreated. All test fields were exposed to photoactivating blue light 1 h after each UV exposure. As shown by a newly established specific PLE test score (AA + SI + 0.4P [range, 0-12], where AA is affected area score [range, 0-4], SI is skin infiltration score [range, 0-4], and P is pruritus score on a visual analogue scale [range, 0-10]), PLE symptoms were significantly fewer on test sites treated with active AS lotion than on untreated (P = 0.00049) or placebo-treated test sites (P = 0.024). At 144 h after first UV exposure (the time point of maximal PLE symptoms), the mean test scores for untreated, active AS lotion-treated, and placebo-treated test fields were 4.39, 1.73 (61% reduction; 95% confidence interval (CI), 36% to 85%), and 3.20 (27% reduction; 95% CI, 3% to 51%), respectively. Pretreatment with SPF30 sunscreen completely prevented PLE symptoms in all patients. The present results indicate that DNA damage may trigger PLE and that the application of topical liposomes containing DNA repair enzymes to increase DNA repair may effectively prevent PLE.