Hao Ou-Yang

Objective: Sweating plays a critical role in maintaining thermal balance and keeping skin cool during exercise. People often wear sunscreens on hot summer days for sun protection. Most recreational sunscreens are designed to be water‐ and sweat‐resistant, so that sweating will not remove or compromise the protection. The objective of this study was to determine whether wearing sweat‐resistant sunscreen might impede natural sweating, potentially interfering with thermal regulation and resulting in the elevation of skin temperature.Methods: We conducted a controlled, randomized, split‐face and split‐arm clinical study with 24 female subjects wearing an SPF 70 lotion sunscreen on half of the face and an SPF 70 spray sunscreen on one of the forearms at a dosage of 2 mg cm⁻². Following sunscreen application, subjects participated in two sessions of indoor exercise to induce clearly visible sweating.Results: We found that both skin temperatures and sweat evaporation rates were significantly elevated after each session, yet there were no significant differences in either skin temperatures or sweat rates between the treated and untreated control sites at any time point for any of the skin sites measured.Conclusion: We conclude that the application of tested sweat‐resistant sunscreen lotions and sprays does not have any measurable effects on skin cooling by natural sweating process. People should continue to use these sunscreens during recreational activities.

Solar protection is an important public health issue because solar UV exposure can cause acute and chronic damage to the skin. Seeking shade is a convenient and commonly practiced sun avoidance measure. Shade works by physically shielding the skin from direct UV rays; however UV rays can also reach the skin from other angles. It is not clear how protective the widely-used shade structures like umbrellas and walls are under actual use conditions. In this study, a sky view model was applied to systematically assess the influence of different factors to umbrellas and walls, including the transmission of the shade materials, the reflectivity of the ground or the wall, diffused UV to total UV irradiance ratios, shade geometry, a person's positions and orientations in the shade. We measured the sunburn protection factor (SPF) with a calibrated UV meter at different positions in the shades of an umbrella at different times of the day and compared the measurement results with the modeling. We found that shade structures like umbrellas and walls are more effective when the ratios of diffused UV to total UV irradiance are smaller (mid-day). The effectiveness increases with more coverage, less surface reflectance, and more centralized positions in the shade. The SPF value for a typical umbrella is probably between 3 and 7 in real-life. The low sun protection level offered by a typical shade highlights the importance of educating the public about how to properly protect the skin from the sun and the importance of applying a combination of sun protection measures during extended sun exposures.

Background: The efficacy of sunscreen is evaluated by SPF values, which are quantitatively determined in laboratories on the backs of human subjects according to a standardized procedure. However, SPF cannot be directly translated to sunburn protection under real-life situations because actual efficacy depends on various factors related to human behaviors and environmental conditions. This study clinically evaluated the efficacy of two sunscreen sprays (SPF 30 and SPF 70) under natural sunlight exposure on healthy subjects at the beach. Methods: Twenty subjects were divided into two cells for the two sunscreen sprays (SPF 70 and SPF 30) in a single-center, actual usage test. The primary endpoint of the study was sunburn protection on the dorsal arms and the secondary endpoint was protection on the face and neck. Subjects stayed at the beach for 4 h after application of the sunscreens with normal beach activities. Subjects’ behavior at the beach, the amounts of sunscreen applied and reapplied, and environmental conditions were all recorded. Results: There was no significant sunburn for a majority of the subjects in either cell. However, neither sunscreen completely blocked the sunburn, especially the face/neck area. We found that the SPF 70 sunscreen was more effective than the SPF 30 sunscreen. Conclusion: Modern sunscreen sprays, applied liberally, are effective in providing sunburn protection for the body in a beach setting.

Background: The efficacy of sunscreen is evaluated by SPF values, which are quantitatively determined in laboratories on the backs of human subjects according to a standardized procedure. However, SPF cannot be directly translated to sunburn protection under real-life situations because actual efficacy depends on various factors related to human behaviors and environmental conditions. This study clinically evaluated the efficacy of two sunscreen sprays (SPF 30 and SPF 70) under natural sunlight exposure on healthy subjects at the beach. Methods: Twenty subjects were divided into two cells for the two sunscreen sprays (SPF 70 and SPF 30) in a single-center, actual usage test. The primary endpoint of the study was sunburn protection on the dorsal arms and the secondary endpoint was protection on the face and neck. Subjects stayed at the beach for 4 h after application of the sunscreens with normal beach activities. Subjects’ behavior at the beach, the amounts of sunscreen applied and reapplied, and environmental conditions were all recorded. Results: There was no significant sunburn for a majority of the subjects in either cell. However, neither sunscreen completely blocked the sunburn, especially for the face/neck area. We found that the SPF 70 sunscreen was more effective than the SPF 30 sunscreen. Conclusion: Modern sunscreen sprays, applied liberally, are effective in providing sunburn protection for the body in a beach setting.

Extended water exposure can cause stratum corneum swelling and a more porous skin barrier. People often wear water-resistant sunscreen formulations during extended period of water activities in the summer to protect skin from harmful UV rays. We wanted to evaluate whether sunscreen formulations can also serve as additional water barriers to help mitigate the disruption in stratum corneum caused by constant exposure to water. We conducted trans-epidermal water loss (TEWL) measurement in a controlled water patch (including salt and chlorine water) model and then applied this relevant model to study the effects of pre-treatments of sunscreen sprays and stick. We also conducted water sorption–desorption test in vivo with and without sunscreens. Finally, we studied the effect of constant water exposure combined with a known irritant, sodium lauryl sulphate (SLS), in a randomized clinical trial. We found that application of sunscreen formulations help mitigate water-induced barrier disruption by repelling water at skin surface. Pre-treatment of sunscreen also statistically decreased the irritation in an acute patch test model. Hydrophobic sunscreen formulations can help protect skin from extended water exposure by serving as additional water barriers. l'exposition prolongée à l'eau peut provoquer un gonflement de la couche cornée et donc conduire à une barrière plus poreuse de la peau. Les gens portent souvent en été des formulations de protection solaire résistantes à l'eau pendant des périodes prolongées d'activité dans l'eau pour protéger la peau contre les rayons UV nocifs. Nous voulions évaluer si des formulations de protection solaire peuvent également servir de barrières supplémentaires à l'eau pour aider à atténuer les perturbations dans le stratum corneum causées par une exposition constante à l'eau. Nous avons effectué des mesures de la perte en eau transépidermique (PIE) dans un modèle contrôlé de patch à l'eau (y compris de l'eau salée et chlorée); ensuite nous avons appliqué ce modèle pertinent pour étudier les effets de prétraitements par des produits de protection solaire vaporisés ou appliqués sous forme de bâton. Nous avons également procédé à un essai de sorption-désorption d'eau in vivo avec et sans filtres solaires. Enfin, nous avons étudié l'effet de l'exposition constante à l'eau combinée avec un irritant connu, le sodium lauryl sulfate (SLS) dans un essai clinique randomisé. Nous avons trouvé que les applications des formulations des crèmes solaires aident à atténuer la rupture de la barrière induite par l'eau en repoussant l'eau à la surface de la peau. Le prétraitement avec la crème solaire diminue aussi l'irritation de manière statistiquement significative dans le modèle de test du patch aiguë. Les formulations de protection solaire hydrophobes peuvent aider à protéger la peau contre l'exposition prolongée à l'eau en servant d'obstacles supplémentaires.

Summary: Background: Advances in sunscreen technologies have yielded broad spectrum sunscreens at high‐sun protection factor (SPF) and ultraviolet A protection factor (UVA‐PF) levels that are photostable and powerful in protecting skin from erythema. Questions arise whether these sunscreens protect proportionally against cellular skin damage caused by high ultraviolet exposures.Objective: The objective of this study is to evaluate if high‐SPF sunscreen can protect skin at a cellular level under UV exposure doses [> 50 minimal erythema dose (MED)] similarly to the SPF value.Methods: Sunburn cells, Langerhans cells, thymine dimers, protein 53 (p53), and matrix metalloproteinase (MMP)‐1 and MMP‐9 endpoints were evaluated in biopsies from 12 subjects following four treatments: unprotected exposed to 0, 1 and 3 MED and sunscreen (SPF 55) protected exposed to 55 MED of UV radiation.Results: All the markers showed significantly more damage for the 3 MED‐untreated sites when compared with non‐irradiated control, and majority of the markers showed marked damage following unprotected 1 MED exposure. After 55 MEDs, sunscreen‐protected sites showed significantly less p53 and MMP‐9 (keratinocyte) staining than the 1 MED‐exposed unprotected sites, while all the other biomarkers in sunscreen protected sites showed no statistical differences from 1 MED‐exposed unprotected sites.Conclusions: A high‐SPF photostable sunscreen with high UVA‐PF can provide proportionately high protection against multiple cellular damage markers.

Background: High sun protection factor (SPF) sunscreens have multiple benefits but there has not been validation of the test method for determining SPF values higher than 50. This study addresses specifically the accuracy and reproducibility of the high SPF test.Methods: Two high SPF formulations with a standard reference (SPF 15) were tested at four independent test facilities according to the 2007 FDA proposed amendments to the sunscreen monograph. Statistical analysis was performed to compare the SPF results within each lab as well as the SPF results between different labs.Results: The test formulations have overall mean values of 90.5 and 70.7. There was no statistically significant difference between the labs for either formulation and all four labs were able to statistically differentiate these two levels of SPF values. The coefficients of variance (CV) for the high SPF formulations were comparable to those of the corresponding SPF 15 reference within each lab.Conclusions: The data show that SPF values above 50 and up to at least 90 can be measured by multiple laboratories with accuracy and reproducibility.