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

OBJECTIVE: To propose a strategy for using sunscreens that optimizes the balance between skin health and adverse effects to humans and the environment. METHODS: A model was developed to explore the relationship between sunscreen usage and personal sun exposure throughout the year in populations resident at different latitudes. RESULTS: There is little biological justification in terms of skin health for applying sunscreen over the 4-6 winter months at latitudes of 45° N and higher, whereas year-round sunscreen is advised at latitudes of 30° N and lower. Avoiding sunscreen application at times when it is biologically unnecessary results in an annual reduction in sunscreen use of 25%. Furthermore, using products containing UV filters over the winter months at more northerly latitudes could lead to a higher number of people with vitamin D deficiency. The single largest use of sunscreen is on a sun-seeking holiday and encouragement to make more use of clothing and shade would appreciably reduce the sunscreen burden to the environment. CONCLUSION: We need to use sunscreens wisely so that we gain the health benefit from their use while at the same time limiting possible harm to ourselves and the environment.

OBJECTIF: Proposer une stratégie d'utilisation des protections solaires qui optimise l'équilibre entre la santé de la peau et les effets indésirables pour l'homme et l'environnement. MÉTHODES: Un modèle a été développé pour explorer la relation entre l'utilisation de crème solaire et l'exposition au soleil toute l'année pour des populations vivant à différentes latitudes. RÉSULTATS: En ce qui concerne la santé de la peau, l'application de crème solaire pendant les 4 à 6 mois d'hiver se justifie peu sur le plan biologique à des latitudes de 45° N et plus, alors qu'elle est conseillée toute l'année à des latitudes de 30° N et moins. L'absence d'utilisation de crème solaire à des moments où cela est inutile sur le plan biologique permet de réduire l'utilisation de crème solaire de 25 % par an. Par ailleurs, l'utilisation de produits contenant des filtres UV les mois d'hiver à des latitudes plus nordiques pourrait conduire à un nombre plus élevé de personnes carencées en vitamine D. L'utilisation la plus importante de protection solaire a lieu lors d'un voyage où l'on cherche là s'exposer au soleil, et l'incitation à se protéger davantage à l'aide de vêtements et de l'ombre réduirait sensiblement l'impact des produits de protection solaire sur l'environnement. CONCLUSION: Nous devons utiliser judicieusement les produits de protections solaires afin que leur utilisation apporte un bénéfice pour la santé tout en limitant les risques potentiels pour nous-mêmes et pour l'environnement.

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.

Sunscreen and the Precautionary Principle.

The Precautionary Principle is a decision-making device designed to help us when we deal with uncertain risks. Despite a number of case-control and prospective studies over several years, there remains some uncertainty as to whether sunscreens are unequivocally effective in reducing the risk of skin cancer, and we examine how useful the principle is in deciding whether sunscreen should be included in the sun protection toolbox as a public health measure. We conclude that the Precautionary Principle can be a useful tool supporting public health recommendations to use sunscreen as a means of reducing the morbidity and mortality of skin cancer, but we show that it is not without its shortcomings.

Natural and Simulated Solar Radiation.

The extra-terrestrial solar spectrum corresponds approximately to a black body of temperature about 5,800 K, with the ultraviolet region accounting for almost 8% of the total solar energy. Terrestrial solar spectral irradiance peaks at around 500 nm in the blue-green region, whereas the diffuse component peaks in the UVAI-blue region of the spectrum, with the infrared component comprising almost entirely direct radiation. Several factors impact on the magnitude and spectral profile of terrestrial solar spectral irradiance, and these include solar elevation, reflection from land and sea, air pollution, altitude above sea level and cloud cover. Measurements of erythemal UV from a number of ground-based networks around the world indicate an approximate 4-fold difference in ambient annual exposure between Australia and countries in northern Europe. In the absence of measured data, models to compute solar UV irradiance are a useful tool for studying the impact of variables on the UV climate. Simulated sources of sunlight based on a xenon arc lamp can be configured to give a close match to the spectral output of natural sunlight at wavelengths less than about 350 nm, and these are invaluable in the laboratory determination of sunscreen performance, notably the Sun Protection Factor (SPF). However, the divergence -between natural and simulated solar spectra at longer wavelengths may explain why SPFs measured in natural sunlight are less than those determined in the laboratory.

Erythema and Acclimatization Following Repeated Sun Exposure: A Modeling Study.

The development of a computational model is described that allows time-varying erythema and acclimatization to be determined following repeated exposure to solar ultraviolet (UV) radiation. Good agreement was observed between experimental data and model predictions. Results are presented that illustrate how daily, adventitious sun exposure over the course of a year can result in occasional erythema generally in the late spring/early summer, while at the same time showing how the photoadaptive response of the skin changes throughout the year at different latitudes and for different sun-reactive skin types. The model is predicated on three physiological responses; the erythemal response as a function of increasing UV dose, the time courses of erythema and adaptation in response to a single UV exposure. Mathematical models complement observational data and the outputs from the model may help in planning future experimental studies, as well as providing insights into mechanistic responses.

Correction: A library of action spectra for erythema and pigmentation.

Correction for 'A library of action spectra for erythema and pigmentation' by Alois W. Schmalwieser et al., Photochem. Photobiol. Sci., 2012, 11, 251-268, DOI: .

Drivers for Sun Protection in Black South Africans.

Sun protection behavior studies are almost exclusively carried out in populations with fair skin for the obvious reason that people with unpigmented skin are more susceptible to the health impacts of excess solar ultraviolet radiation exposure. In a dataset of 1271 Black South Africans, we analyzed factors related to sun protection applied when spending time outdoors including awareness of skin cancer, gender, age and Living Standards Measure (LSM) where 1-4 equate to the lowest, 5-7 intermediate and 8-10 the highest LSM status. The most important driver for Black South Africans to use sun protection was whether they were aware of skin cancer (OR: 2.6 for those who were aware versus those who were not, P < 0.0001). Sunscreen was preferred by respondents in LSM 8-10 whereas people in the lowest group (LSM 1-4) favored shade, umbrellas and hats. One in two respondents claimed to use some form of sun protection, which appears to be higher than deeply pigmented populations in other countries.

The Impact of Sunlight on Adventitious Buying and Giving.

The impact of sunlight on the income derived from spending and donations in a coastal charitable facility is examined. Data consisted of income during 2017 and 2018, together with daily sunshine hours and apparent temperature, and a multiple linear regression model was employed to determine the importance of these meteorological variables on income. Results indicated that income increased with both increasing sunshine hours and apparent temperature, but with an interaction effect (negative coefficient) between sunlight and apparent temperature such that the effect of sunlight on income is positive at lower apparent temperatures and negative at higher apparent temperatures. So, besides its many direct and indirect effects on man, it appears that sunlight also acts as a positive driver in adventitious giving and buying.

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.

Labelled sunscreen SPFs may overestimate protection in natural sunlight.

Limited evidence exists to indicate that sunscreen protection factors determined in the laboratory are higher than those in natural sunlight. In this article we propose an explanation for this difference and estimate the expected SPFs of sunscreen products in natural sunlight and those expected from laboratory testing. Our results indicate that the labelled SPF, determined by in vivo assay using a UV solar simulator, overestimates the SPF that would be expected in natural sunlight to the extent that for products labelled SPF50+, it may not be possible to achieve a protection against sunlight of more than 25-fold. The popular interpretation of the SPF that it can be thought of as how much longer skin covered with sunscreen takes to burn in sunlight compared with unprotected skin, can no longer be defended.

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.

An appraisal of the need for infrared radiation protection in sunscreens.

Many sunscreens incorporate agents that are said to protect against infrared (IR) damage in the skin but we lack any real data on their benefit in the context of normal human behaviour in the sun. The object of this study was to examine typical IR exposure levels to the sun and industrial sources in order to decide whether there is a need for sunscreens to contain agents that protect against IR radiation, specifically the IR-A waveband. We reviewed claims currently made by products offering protection against IR-A and studies on the biological and clinical effects attributed to IR-A, and compared IR-A exposure levels from these studies with those typically received from the sun and from industrial sources. We found that annual levels of IR-A exposure resulting from typical behaviour in the sun are commensurate with those experienced occupationally by workers exposed to industrial sources of IR, such as steel and glass furnaces. Yet these workers appear to suffer little in the way of chronic skin damage. We conclude that there is not compelling evidence to demonstrate that observable, deleterious cutaneous effects are occurring at doses of solar IR radiation corresponding to those experienced by populations in their normal environments and for this reason we believe it is premature to incorporate IR protection into topical sunscreens and to make claims related to ageing of the skin that consumers may expect to see.