Uli Osterwalder

Photoprotection: Part II. Sunscreen: Development, efficacy, and controversies

In addition to the naturally occurring, physical, and systemic photoprotective agents reviewed in part I, topical ultraviolet radiation filters are an important cornerstone of photoprotection. Sunscreen development, efficacy, testing, and controversies are reviewed in part II of this continuing medical education article.

Global state of sunscreens

The use of sunscreen is embedded in a hierarchy of sun protection strategies consisting primarily of sun avoidance by seeking shade and covering up with clothing. Sunscreens are, however, important means of protection; thus, understanding how they work and knowing their limitations are crucial. This review explains the role of ultraviolet (UV) filters, emollients, emulsifier systems and other components in a sunscreen, as well as trends in formulations in Europe, North America, Latin America, and Asia Pacific. Furthermore, it explains how sunscreen performance in terms of sun protection factor, UVA protection, and other metrics can be simulated. The role of sensory characteristics in assessing and improving compliance is also discussed. In the final chapter, Facts and Fiction, five of the most common myths about sun exposure and sun protection by sunscreen are debunked.

Photoprotection: Part I. Photoprotection by naturally occurring, physical, and systemic agents

The acute and chronic consequences of ultraviolet radiation on human skin are reviewed. An awareness of variations in naturally occurring photoprotective agents and the use of glass, sunglasses, and fabric can lead to effective protection from the deleterious effects of ultraviolet radiation. New systemic agents, including Polypodium leucotomos, afamelanotide, and antioxidants have potential as photoprotective agents.

Ex vivo evaluation of radical sun protection factor in popular sunscreens with antioxidants.

BACKGROUND UVA induces tissue damage via the production of radical oxygen species. Adding antioxidants to UV filters in sunscreens is a novel photoprotective strategy. The topical application of antioxidants in sunscreen can potentially neutralize the UVA-induced free radicals. OBJECTIVES We sought to assess the degree of free radical protection offered by sunscreens with antioxidants and attempted to differentiate the contribution of free radical protection from that of the UV filters. METHOD Twelve sunscreen products were purchased. The degree of UVA protection (UVA-PF) was measured via an in vitro assay according to a European guideline (Colipa). In addition, an electron spin resonance (ESR) spectroscopy-based assay was used to measure the radical skin protection factor (RSF) and antioxidant power (AP) of each product. RESULTS The sun protection factor (SPF) values of the sunscreens ranged from 15 to 55, and the UVA-PF values ranged from 2.4 to 28.2. The RSF values ranged from 2.4 to 27.1. There is a high correlation between RSF and UVA-PF. The AP values for nearly all the products were 0, and two products (#4 and #9) had very low AP values of 16 and 12, respectively. LIMITATIONS The study only evaluated a small number of sunscreen products, and only ex vivo and in vitro methods were used to assess the products. CONCLUSIONS The idea of combining UV filters with antioxidants is appealing. Current sunscreen products on the market offer free radical protection, but the majority of the radical protection is from UV filters rather than antioxidants.

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

We lack comparative data on sunscreens with comparable sun protection factors (SPFs), but with different levels of UVA protection, especially against cumulative erythema from repeated suberythemal exposure. Thus, we compared the protection from cumulative sunburn with two sunscreens labeled SPF 6, but with different UVR-absorbing properties, one that absorbs the UVB waveband and the other that absorbs UVB+UVA wavebands. We simulated sunlight typical of temperate latitudes to expose skin daily to suberythemal doses for 13 consecutive days. The study population consisted of eight fair-skinned sun-sensitive healthy young adults. Erythema was assessed by eye and objectively, and the SPF of each sunscreen was modeled with changes in solar UVR with time of day and latitude. The broad-spectrum sunscreen gave much better protection against cumulative erythema than the UVB sunscreen. The explanation for this is that UVA makes a greater contribution toward sunburn at temperate latitudes than under the laboratory conditions in which SPF is tested and assigned. The data support the current trend toward broad-spectrum sunscreen protection. They also show that labeled SPF is much more reliable with broad-spectrum sunscreens because SPF with primarily UVB sunscreens is dependent on time of day and latitude.

Simulation of sunscreen performance

Abstract Sunscreens are used to protect the human skin against harmful effects of solar UV radiation. The most important quantity characterizing sunscreen performance is the sun protection factor (SPF). At the stage of development of new sun protection formulations quick and inexpensive methods for estimation of the UV screening performance are highly desirable. The most convenient approach towards this goal is given by computational simulations. Models for the calculation of the SPF employ the same algorithm as used with in vitro SPF measurements, but replace the transmittance measurement by the calculation of the overall absorbance of the UV filters in an irregular sunscreen film. The simulations require a database with quantitative UV extinction spectra of the relevant UV filters as well as a mathematical description of the film irregularity. The simulation algorithm implies also the consideration of photodegradation properties of the UV filters in the sunscreen composition. Besides using such simulations for designing new sunscreen formulations, the calculations can also support the understanding of sunscreen performance in general.

Comparison of ultraviolet A light protection standards in the United States and European Union through in vitro measurements of commercially available sunscreens

Background The importance of adequate ultraviolet A light (UVA) protection has become apparent in recent years. The United States and Europe have different standards for assessing UVA protection in sunscreen products. Objective We sought to measure the in vitro critical wavelength (CW) and UVA protection factor (PF) of commercially available US sunscreen products and see if they meet standards set by the United States and the European Union. Methods Twenty sunscreen products with sun protection factors ranging from 15 to 100+ were analyzed. Two in vitro UVA protection tests were conducted in accordance with the 2011 US Food and Drug Administration final rule and the 2012 International Organization for Standardization method for sunscreen effectiveness testing. Results The CW of the tested sunscreens ranged from 367 to 382 nm, and the UVA PF of the products ranged from 6.1 to 32. Nineteen of 20 sunscreens (95%) met the US requirement of CW >370 nm. Eleven of 20 sunscreens (55%) met the EU desired ratio of UVA PF/SPF > 1:3. Limitations The study only evaluated a small number of sunscreen products. Conclusion The majority of tested sunscreens offered adequate UVA protection according to US Food and Drug Administration guidelines for broad‐spectrum status, but almost half of the sunscreens tested did not pass standards set in the European Union.

Sun Protection Factor Communication of Sunscreen Effectiveness: A Web-Based Study of Perception of Effectiveness by Dermatologists

Sun Protection Factor Communication of Sunscreen Effectiveness: A Web-Based Study of Perception of Effectiveness by Dermatologists The sun protection factor (SPF) is commonly used to convey a sunscreen’s effectiveness in protecting against UV radiation that causes sunburn (ie, erythema-inducing radiation [EIR]).1 Importantly, the EIR burden depends on the proportion of EIR actually transmitted through the sunscreen to the skin (% EIR transmitted) and not on the proportion of EIR absorbed by the sunscreen (% EIR absorbed). Doubling SPF from, say, 30 to 60 halves % EIR transmitted from 3.3% to 1.7%, thus doubling protection2 (Figure, A). Unfortunately, however, media and health professionals often incorrectly state that SPFs beyond 30 offer only minor improvements in sun protection, arguing that the increase in % EIR absorbed by the sunscreen is less pronounced than the corresponding increase in SPF values3,4 (eg, 96.7% < 98.3% vs 30 60). However, only changes in % EIR transmitted directly relate to changes in SPF; changes in % EIR absorbed do not. In this study, we evaluated whether dermatology experts are able to adequately assess improvements in sunscreen effectiveness based on the following information formats: SPF vs % EIR absorbed vs % EIR transmitted.

Calculation of the sun protection factor of sunscreens with different vehicles using measured film thickness distribution - Comparison with the SPF in vitro.

The sun protection factor (SPF) depends on UV filter composition, and amount and type of vehicle of the applied sunscreen. In an earlier work, we showed that the vehicle affected the average thickness of sunscreen film that is formed upon application to a skin substrate and that film thickness correlated significantly with SPF in vitro. In the present study, we quantitatively assess the role for sunscreen efficacy of the complete film thickness frequency distribution of sunscreen measured with an oil-in-water cream, an oil-in-water spray, a gel, a water-in-oil, and an alcoholic spray formulation. A computational method is employed to determine SPF in silico from calculated UV transmittance based on experimental film thickness and thickness distribution, and concentration and spectral properties of the UV filters. The investigated formulations exhibited different SPFs in vitro and different film thickness distributions especially in the small thickness range. We found a very good agreement between SPF in silico and SPF in vitro for all sunscreens. This result establishes the relationship between sun protection and the film thickness distribution actually formed by the applied sunscreen and demonstrates that variation in SPF between formulations is primarily due to their film forming properties. It also opens the possibility to integrate the influence of vehicle into tools for in silico prediction of the performance of sunscreen formulations. For this, the use of the Gamma distribution was found to be appropriate for describing film thickness distribution.

Suntanning with sunscreens: a comparison with sunbed tanning

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.