Is sunscreen alone effective at preventing sunburn on a high-solar beach vacation: A modeling study?

Beach holidays in areas of strong sunlight are popular and sunscreen is often the primary means of photoprotection favored by many people. The object of this study was to estimate how effective sunscreen is in preventing sunburn under high ultraviolet (UV) levels. We used a computational model to determine how the quantity, frequency, substantivity, and labeled SPF of applied sunscreens impact on the predicted erythemal response in unacclimatized skin over the course of a 7-day holiday in a high-solar environment. Our results indicated that sunscreen on its own may be insufficient to prevent sunburn in white skin on a sun-seeking holiday that combines prolonged exposure with high UV levels. Nevertheless, sunscreens have a valuable role to play on a beach holiday especially if an SPF30 or higher is chosen, the product is applied liberally and uniformly, application is started early into the sun exposure period and repeated at 2-hourly intervals throughout the day, and the product binds well to the skin. The main limitation of our investigation is that it is not an observational study but rather a computational model and while all models are wrong, some, including this one, are useful.

Sunburn and sun protection in black skin.

BACKGROUND: People with black skin are much less susceptible to sunburn than white-skinned individuals, yet there are scarce data on self-reported incidence of sunburn and sun protection measures in people with deeply-pigmented skin. METHOD: An on-line survey tool was used to collect self-assessed data about demographic variables, sunburn incidence, and use of sun protection modalities. RESULTS: Two-thirds of respondents with black skin living in the UK claimed never to have been sunburnt; a much higher proportion than those living in South Africa and Nigeria where 34 and 46%, respectively, reported never experiencing sunburn. Similar results were seen in the reported use of sun protection measures between the countries with two-thirds of black people living in the UK claiming they never used any form of sun protection compared with about one-third of Black Africans. Black people living in the UK were more likely to use sunscreen as a form of sun protection, whereas sunscreen was the least popular modality in the two African countries with shade being the most common form of limiting sun exposure. CONCLUSION: The findings provide some insight into the complexities of skin color perception, incidence of sunburn, and sun protection use among people with deeply-pigmented skin living in three countries with large differences in the solar UV environment.

Time and Place as Modifiers of Personal UV Exposure.

It is a common belief that, if we want to limit our sun exposure during outdoor recreational activities and holidays in order to avoid sunburn or reduce our risk of skin cancer, we need to reach for the bottle of sunscreen or cover up with clothing. As important as these measures are, there is another way to enjoy our time outdoors and still benefit from the experience. In this article, we consider the impact of time, place, and behaviour outdoors on our exposure to solar ultraviolet (UV) radiation. Some of the simple actions we can take in controlling our UV exposure include being aware of the position of the sun in the sky, understanding how we can use the UV index to guide our outdoor exposure, and the importance of reducing our sun exposure around the middle of the day. Finally we review our preferred holiday activities and destinations, and the influence of outdoor leisure pursuits. By planning where and when we spend our leisure time in the sun, we can maximise our enjoyment whilst limiting our UV exposure.

Sunburn at the seaside.

BACKGROUND/PURPOSE: The purpose of this paper is to estimate the contribution to our erythemal exposure at the coast of solar ultraviolet (UV) both reflected from, and transmitted into, the ocean. METHODS: The reflection of solar UV radiation from, and transmitted into, seawater was calculated using a numerical model under a number of atmospheric conditions to estimate erythemal exposure on the skin of supine/prone and ambulant people. RESULTS: The results were expressed as UV Indices. Even under the most extreme insolation with the sun directly overhead, where the ambient UV Index may be around 14, reflected UV from the ocean contributes an erythemal exposure to the skin equivalent to a UV Index of about 0.7. For typical ocean waters, with the sun high in the sky, the UV index within the water is about 7 at a depth of 2 m. CONCLUSION: Whilst our eyes often sense a high level of reflected sunlight from the ocean, especially when the sun is low in the sky, our skin does not share that experience. The reason people get sunburnt at the seaside has more to do with the absence of shade than with reflectance by the water surface or even beach sand.

Melanin distribution in human epidermis affords localized protection against DNA photodamage and concurs with skin cancer incidence difference in extreme phototypes.

Epidermal DNA damage, especially to the basal layer, is an established cause of keratinocyte cancers (KCs). Large differences in KC incidence (20- to 60-fold) between white and black populations are largely attributable to epidermal melanin photoprotection in the latter. The cyclobutane pyrimidine dimer (CPD) is the most mutagenic DNA photolesion; however, most studies suggest that melanin photoprotection against CPD is modest and cannot explain the considerable skin color-based differences in KC incidence. Along with melanin quantity, solar-simulated radiation-induced CPD assessed immediately postexposure in the overall epidermis and within 3 epidermal zones was compared in black West Africans and fair Europeans. Melanin in black skin protected against CPD by 8.0-fold in the overall epidermis and by 59.0-, 16.5-, and 5.0-fold in the basal, middle, and upper epidermis, respectively. Protection was related to the distribution of melanin, which was most concentrated in the basal layer of black skin. These results may explain, at least in part, the considerable skin color differences in KC incidence. These data suggest that a DNA protection factor of at least 60 is necessary in sunscreens to reduce white skin KC incidence to a level that is comparable with that of black skin.-Fajuyigbe, D., Lwin, S. M., Diffey, B. L., Baker, R., Tobin, D. J., Sarkany, R. P. E., Young, A. R. Melanin distribution in human epidermis affords localized protection against DNA photodamage and concurs with skin cancer incidence difference in extreme phototypes.

The Solar Ultraviolet Environment at the Ocean.

Atmospheric and oceanic radiative transfer models were used to compute spectral radiances between 285 and 400 nm onto horizontal and vertical plane surfaces over water. The calculations kept track of the contributions by the sun's direct beam, by diffuse-sky radiance, by radiance reflected from the sea surface and by water-leaving radiance. Clear, hazy and cloudy sky conditions were simulated for a range of solar zenith angles, wind speeds and atmospheric ozone concentrations. The radiances were used to estimate erythemal exposures due to the sun and sky, as well as from radiation reflected by the sea surface and backscattered from the water column. Diffuse-sky irradiance is usually greater than direct-sun irradiance at wavelengths below 330 nm, and reflected and water-leaving irradiance accounts for <20% of the UV exposure on a vertical surface. Total exposure depends strongly on solar zenith angle and azimuth angle relative to the sun. Sea surface roughness affects the UV exposures by only a few percent. For very clear waters and the sun high in the sky, the UV index within the water can be >10 at depths down to two meters and >6 down to 5 m.

Ultraviolet erythema: dose response and mediator diffusion.

The earliest contribution made by Jan van der Leun to the field of photobiology was studying the mechanism of UV-induced erythema in human skin - a subject he chose for his PhD in the 1960s. His contribution to this topic encouraged us to continue this work and over a number of years in the 1980s and 1990s, we carried out several studies on quantitative aspects of UV erythema. A major part of Jan's thesis focused on diffusion processes in UV erythema and his observations led him to conclude that erythema induced by radiation with wavelengths of around 300 nm was due to the actions of a diffusing mediator arising in the epidermis, whereas radiation at shorter wavelengths around 254 nm, caused erythema by exerting a direct effect on the dermal blood vessels. By taking his data and combining them with our own studies on the dose response of UV erythema to radiation of different wavelengths, we were able to show that, contrary to Jan's conclusions, the mediator diffusion theory he developed did indeed predict that both UVB and UVC induced erythema could be explained by the action of diffusing mediators.

Age-specific acceleration in malignant melanoma.

Background: The overall incidence of melanoma has increased steadily for several years. The relative change in incidence at different ages has not been fully described.  Objective: To describe how incidence at different ages has changed over time and to consider what aspects of tumour biology may explain the observed pattern of change in incidence.  Methods: The slope of incidence vs age measures the acceleration of cancer incidence with age. We described the pattern of change over time in the overall incidence of melanoma, as well as in acceleration. We used data for males and females from 3 different countries in the 17 sequential 5-year birth-cohort categories from 1895-99 to 1975-79, from which we derived the incidence patterns.  Results: Over time, there has been a tendency for the overall incidence of melanoma to increase and for the acceleration (slope) of the age-incidence curves to decline. The changing patterns of melanoma incidence and acceleration differ between males and females and between the countries analysed.  Conclusions: The observed pattern in melanoma of rising incidence and declining acceleration occurs in other cancers in response to genetic knockouts of mechanisms that protect against cancer. Perhaps some protective mechanism with respect to melanoma may be less effective now than in the past, possibly because of more intense environmental challenges.

Suntanning with sunscreens: a comparison with sunbed tanning.

BACKGROUND/PURPOSE: Acquiring a tanned skin, either by sunbathing, sunbed use, or a combination of both, is a desirable objective for many people. The objective here was to compare the ultraviolet (UV) exposure resulting from a 2-week vacation spent sunbathing with sunscreen-protected skin, with that from a typical course of 10 sessions on a sunbed. METHODS: A numerical analysis combining data on sunlight and sunbed UV levels, time spent tanning and spectral absorption properties of different types of sunscreen. RESULTS: The analysis showed that unless a sunscreen provides optimal broad-spectrum protection, a 2-week sunbathing vacation that avoids sunburn on sunscreen-protected skin can result in a higher cumulative UV exposure than a typical 10-session sunbed course. The lowest exposures for a given sun protection factor (SPF) are obtained when sunscreen delivers broad-spectrum protection that approaches the ideal of uniform absorption at all wavelengths throughout the UV spectrum. CONCLUSION: In extreme cases of recreational sun exposure where sunscreens providing suboptimal broad-spectrum protection are used, the UV insult to the skin is likely to result in higher cumulative exposures than commonly employed sunbed practices.

Determination of the Action Spectrum of UVR-Induced Mitochondrial DNA Damage in Human Skin Cells.

Biological responses of human skin to UVR including cancer and aging are largely wavelength-dependent, as shown by the action spectra of UVR-induced erythema and nuclear DNA (nDNA) damage. A molecular dosimeter of UVR exposure is therefore required. Although mitochondrial DNA (mtDNA) damage has been shown to be a reliable and sensitive biomarker of UVR exposure in human skin, its wavelength dependency is unknown. The current study solves this problem by determining the action spectrum of UVR-induced mtDNA damage in human skin. Human neonatal dermal fibroblasts and primary human adult keratinocyte cells were irradiated with increasing doses of UVR. Dose-response curves of mtDNA damage were produced for each of the UVR sources and cell types, and an action spectrum for each cell type was determined by mathematical induction. Similarities between these mtDNA damage action spectra and previously determined nDNA damage were observed, with the most detrimental effects occurring over the shorter UVR wavelengths. Notably, a statistically significant (P<0.0001) greater sensitivity to mtDNA damage was observed in dermal fibroblasts compared with keratinocytes at wavelengths >300 nm, possibly indicating a wider picture of depth dependence in sensitivity. This finding has implications for disease/photodamage mechanisms and interventions.

Modelling vitamin D status due to oral intake and sun exposure in an adult British population.

A mathematical model is described for estimating changes in plasma 25-hydroxyvitamin D (25(OH)D) levels throughout the year as a consequence of varying the oral intake of vitamin D and the behaviour outdoors of white British adults resident in different regions of the UK. The model yields seasonal and geographical patterns of 25(OH)D concentrations that agree closely with observational studies. Use of the model allows estimates to be easily made of the sun exposure and oral intake necessary to avoid vitamin D deficiency in defined proportions of the population, as well as strategies that would lead to vitamin D sufficiency throughout the year. The analysis demonstrates that addressing concerns about insufficient vitamin D levels, especially during the winter, may be achieved by modifying oral vitamin D intake over the winter, increasing summer sun exposure or a combination of both.

The ideal spectral profile of topical sunscreens.

Sunscreens were originally designed to prevent sunburn and incorporated active ingredients that absorbed principally in the UVB region. However, over the past 20 years or so new ingredients have been developed that extend absorption across a much wider range of the solar ultraviolet spectrum in the belief that sunscreens should provide balanced spectral absorption. This article develops the rationale for spectral uniformity by showing that this requirement is aligned to more natural forms of photoprotection. It is shown that a modern sunscreen can provide a spectrally balanced absorption profile in line with shade and many types of clothing fabric. Finally, a new metric is introduced that measures how well the spectral absorption profile of topical sunscreens performs against this ideal.

The impact of topical photoprotectants intended for daily use on lifetime ultraviolet exposure.

BACKGROUND: Exposure to solar ultraviolet (UV) radiation is believed to be an important contributor to facial photoaging. Daily application of topical photoprotectants is thought to mitigate this process. OBJECTIVES: To examine the importance of a number of independent factors in reducing the lifetime UV exposure of facial skin achieved by daily use of photoprotective products. METHODS: A behavioral model of solar UV exposure to the face is incorporated with the spectral profile of two different candidate topical products, the age at which regular photoprotection begins, the SPF of the products, and whether the product is applied year-round or just in the summer months to examine the reduction in lifetime UV exposures achieved by daily use of photoprotective products. RESULTS: The results show that regular use of topical photoprotective agents reduces significantly lifetime UV exposure to the face compared with nonuse. Analysis of variance shows that the most important factor is to begin regular daily use early in life. The SPF and spectral profile of the product is of lesser importance, as is whether daily use is confined to the summer months rather than year-round. CONCLUSIONS: While it remains unproven and speculative, there is good reason to suppose that regular use of daily facial topical products containing UV filters, particularly if started early in adult life, will be translated into fewer visible signs of aging later in life.

Skin color change in Caucasian postmenopausal women predicts summer-winter change in 25-hydroxyvitamin D: findings from the ANSAViD cohort study.

CONTEXT: UV radiation is responsible for vitamin D synthesis and skin tanning. Longitudinal data relating skin color to vitamin D status are lacking. OBJECTIVE: Our objective was to determine whether seasonal facial skin color changes are related to changes in 25-hydroxyvitamin D [25(OH)D]. DESIGN AND SETTING: We conducted a prospective observational cohort study (Aberdeen Nutrition Sunlight and Vitamin D) with five visits over 15 months, starting spring 2006 with an additional visit in spring 2008 at a university medical research center in Scotland, 57° N. PARTICIPANTS: Participants included 314 Caucasian postmenopausal women, age 60-65 yr. MAIN OUTCOME MEASURES: Facial skin color was assessed by skin reflectance and expressed as the individual typology angle (ITA) (higher number indicates paler skin). 25(OH)D was measured by immunoassay. RESULTS: Most women (43%) reported Fitzpatrick skin type III (always burns, always tans), 32% type II, and 25% type I (always burns, never tans). Overall, mean (sd) ITA in degrees were 36.6 (7.7), 38.2 (6.5), and 42.8 (5.3), respectively, for summer, autumn, and winter (P < 0.001). Linear regression showed that a 5° summer-winter change in ITA, was associated with a 15 nmol/liter change in 25(OH)D (P < 0.001) but did not predict winter 25(OH)D. Reported sunscreen use was associated with higher 25(OH)D. Mean (SD) 25(OH)D (nanomoles per liter) but not skin color was lower for the top body mass index quartile (Q4) compared with the other quartiles (summer: Q1, 57.1(19.9); Q4, 49.7 (20.4); P = 0.010). CONCLUSIONS: Skin color change between summer and winter predicts seasonal 25(OH)D change. Low vitamin D status in obese women was not due to reduced sun exposure, suggesting that increased requirements or inaccessibility of vitamin D stores may be responsible.

Is casual exposure to summer sunlight effective at maintaining adequate vitamin D status?

BACKGROUND/PURPOSE: The advice that an adequate vitamin D status can be achieved by short, casual exposure to summer sunlight is ubiquitous. This review will examine the value of this advice. METHODS: The results of experimental studies on changes in serum 25-hydroxyvitamin D [25(OH)D] concentrations following ultraviolet exposure are interpreted in the context of human exposure to sunlight. RESULTS: It is shown that current advice about modest sun exposure during the summer months does little in the way of boosting overall 25(OH)D levels, while sufficient sun exposure that could achieve a worthwhile benefit would compromise skin health. CONCLUSIONS: Failure to understand the nature of human exposure to sunlight has led to misguided advice concerning the sun exposure necessary for an adequate vitamin D status.

A randomized comparison of selective broadband UVB and narrowband UVB in the treatment of psoriasis.

UVB is widely used to treat psoriasis. Conventional broadband UVB lamps are less effective than narrowband UVB lamps, which have an emission peak at 311 nm. The long-term safety of narrowband UVB phototherapy is uncertain. "Selective" broadband UVB lamps, which have little emission <290 nm, are also available, but have not been adequately compared to narrowband UVB lamps. We performed a randomized comparison of narrowband UVB (TL-01 lamps) and selective broadband UVB (UV6 lamps) in 100 patients with psoriasis. The median number of exposures for clearance was 28.4 for TL-01 and 30.4 for UV6 (ratio of the medians 0.93; 95% confidence interval (CI) 0.80, 1.09; P=0.39). No significant difference was found in the proportion of patients achieving clearance: TL-01 56%, UV6 40% (odds ratio for clearance with TL-01 relative to UV6 was 2.00 (95% CI 0.87, 4.62), P=0.10). Side effects, including the development of erythema during phototherapy, were similar for the two lamp types. Risk estimates based on the human photocarcinogenesis action spectrum predict that narrowband UVB lamps will be 50% more carcinogenic for equal erythemal doses than selective broadband lamps (UV6). As these two lamp types appear to be of similar efficacy, phototherapy using a selective broadband source may be a safer option than use of narrowband UVB.

Towards optimal regimens for the UVB phototherapy of psoriasis: a mathematical model.

A mathematical model is described that predicts the response of psoriasis to a treatment course of UVB irradiation. The basis of the model is that UVB acts by a direct effect on keratinocytes and that cell cycle arrest is the major mode of action in the phototherapeutic response in psoriasis. Although it is unlikely that UVB causes resolution of psoriatic plaques through a single mechanism, the current model has been based on epidermal cell cycle arrest and entry into the terminal differentiation compartment because this is likely to be a significant rate-limiting factor in determining response to treatment. The model has been validated against results obtained from published clinical studies on narrowband (TL-01) UVB phototherapy for psoriasis. The principal outcomes of the model are that for a given erythemal response, the number of exposures required for clearance is almost independent of the frequency with which patients attend for treatment and that the higher the exposure dose per treatment, the more rapidly will clearance result. The model has been used to suggest optimal regimens for the treatment of outpatients and inpatients.

Sun protection factor determination in vivo using a single exposure on sunscreen-protected skin.

BACKGROUND: Determining sunscreen sun protection factors (SPFs) in a cohort of volunteers, particularly on products designed to provide high levels of protection, can be time-consuming. The conventional approach is to administer to each subject a series of exposures (normally between five and seven) on their sunscreen-protected skin. METHOD: A method, based on Gaussian statistics, is proposed that requires just a single exposure on the sunscreen-protected skin in volunteers to arrive at a reliable estimate of the mean SPF of a test product. RESULTS/CONCLUSION: The method is shown to yield an estimate of a product's mean SPF that is comparable, or better, in accuracy to estimates obtained by conventional multi-exposure testing.