Sunscreens with low sun protection factor inhibit ultraviolet B and A photoaging in the skin of the hairless albino mouse.

We examined the chronic effect of long daily suberythemal, fluorescent solar-stimulated radiation (FSSR; ultraviolet B (UVB)+A(UVA)) and UVA alone on female Skh-1 hairless albino mouse skin. Mice were dorsally irradiated 8 h every weekday for 16 weeks with FSSR or UVA, or 32 weeks with UVA alone. Various topical, low concentration, UVB and/or UVA sunscreens were applied before irradiation. Damage was assessed by skin-fold thickness, histology and biochemically by changes in the proportion of type III collagen. All FSSR-exposed mice showed increased skin thickening, elastic fibre hyperplasia, collagen damage and an increased proportion of type III collagen. Application of the UVB sunscreen (2.00%) resulted in marked protection for all nonbiochemical endpoints. There was no obvious advantage of adding 0.75% UVA sunscreen to the UVB sunscreen, but adding 2.00% UVA sunscreen reduced biochemical changes and connective tissue damage. Sixteen weeks of UVA irradiation caused skin thickening and laxity but the histology and biochemistry were indistinguishable from the controls. The mice irradiated with UVA for 32 weeks showed slight elastic fibre hyperplasia and collagen damage histologically, and increased skin thickening and laxity; these changes were unmodified by the 0.75% UVA sunscreen. These mice showed a significant increase in the proportion of type III collagen against which the UVA sunscreen offered protection. Our data suggest that UVA may be important in photoaging and that the use of low sun protection factor UVB+ UVA sunscreens on a day-to-day basis may offer some protection from solar photoaging.