Paul Robert Tanner

Relevance of UV filter/sunscreen product photostability to human safety.

Photostability or photo‐instability of sunscreen products is most often discussed in undesirable terms with respect to human safety. The health risks, specifically associated with sunscreens, photostable or photo‐unstable, include phototoxic/photoirritation or photoallergic responses and, longer‐term, an increased risk of skin cancers or photoageing. The aims of this paper are to define photostability/photo‐instability and objectively assess the acute and chronic toxicological consequences from the human exposure to UV filter/sunscreens and any probable photo‐degradation products. The reported prevalence of photoirritation and photoallergic responses to sunscreens is rare compared with adverse events, for example, skin irritation or sensitization, produced by cosmetics or topically applied drugs and do not directly implicate potential photo‐degradation products of UV filters. Moreover, for at least one photo‐unstable combination, octyl methoxycinnamate and avobenzone, the long‐term benefits to humans, i.e., reduction in skin cancers, seem to outweigh any potential adverse consequences attributed to photo‐degradation. Sunscreen products are formulated to achieve maximum efficacy which, by necessity and design, incorporate measures to support and promote photostability since all organic UV filters have the potential to photo‐degrade. Current performance measures, in vivo SPF and in vitro UVA, conducted under standardized conditions, in part account for photostability. The concerns expressed when considering human exposure to potential photo‐unstable UV filters or sunscreen products may not manifest as health risks under conditions of use. Still, improvement in sunscreen product photostability continues to be a key strategic objective for manufacturers.

The Controversy of Sunscreen Product Exposure: Too Little, Too Much, or Just Right

Despite decades of human use and clear health benefits, sunscreens remain controversial. At the center of the controversy is exposure. First, what are the data that ad-lib product dosage is below 2 mg/cm2, and, second, what is the evidence that users of sunscreen products under such “real-world” conditions are not protected? It has been suggested that sunscreen products offer little in the way of long-term benefits and may have unintended/unfavorable health consequences by preventing formation of vitamin D or repeatedly exposing humans to harmful chemicals, e.g., ultraviolet (UV) filters. Despite such issues, authoritative organizations in the USA advocate the use of sunscreens along with other photoprotective measures, although the public health messages at times are confusing at the level of the end user, i.e., consumers. Because there are data supportive of the long-term health benefits of daily sunscreen use, arguably the biggest controversy may be the failure to provide an effective public health message amid the relentless criticism of such products. Authorities, such as the American Academy of Dermatology, US Health and Human Services, and Environmental Protection Agency together with Nongovernmental Organizations including Environmental Working Group, should examine the improvement in public health including overall healthcare cost reductions and attempt to deliver a single message akin to the Australian “Slip, Slap, Slop” campaign which has had a favorable public health benefit. One of the pillars of the Australian public health message, “slap” on a sunscreen, will be considered here with respect to exposure and in the context of too little, too much, or just right.