A broad spectrum high-SPF photostable sunscreen with a high UVA-PF can protect against cellular damage at high UV exposure doses.

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.