Albino hairless mice (Skh:HR-1) exposed to sub-erythemal doses of UVB or UVA radiation display physical, visible, and histological alterations. Skin surface replicas, transepidermal water loss, and skin fold thickness were found to change with irradiation. Visibly, the skin wrinkled with UVB and sagged with UVA exposure. These changes were graded on 3-point scales. Histological alterations included tissue thickening, loss of elastic fibers, elastosis, loss of collagen, and increases in mucosubstances. The UVB alterations occur to a much lesser extent with an SPF-15 (7% PABA and 3% oxybenzone) sunscreen product. This sunscreen product had little effect on development of UVAinduced changes. However, an efficient UVA sunscreen (Parsol 1789) did reduce the UVA-induced changes. Many of the UVB-induced alterations regressed after UVB irradiation was stopped. No regression in UVA-induced alterations was observed when UVA irradiation was stopped. Qualitatively, the effects with UVA irradiation were like those observed in mouse chronological aging. These models and the convenient physical and visible grading methods described can be used to determine the effectiveness of topical treatments, such as sunscreens.

Albino hairless mice (Skh: HR-1) exposed chronically to sub-erythemal doses of UV radiation display physical, visible and histological alterations. Using narrow bandwidth radiation covering the UV radiation spectrum from 280-380 nm, the wavelength dependence of these alterations was determined. The wavelength dependence spectra indicate that for all but one parameter measured (skin sagging), UV-B radiation is considerably more efficient than UV-A radiation in producing changes in the skin. However, in natural sunlight there is considerably more UV-A than UV-B radiation, providing the potential for UV-A to have a larger contribution to skin damage than UV-B. This argues in favor of using broad spectrum photoprotective agents to shield the skin adequately from UV-induced aging. The spectra were also used to develop potential associations among events by determining which events occur at similar wavelengths. There seems to be a correspondence between mouse visible skin wrinking (UV-B event) and two histological events: increase in glycosaminoglycans and alteration in collagen. There was no obvious correspondence among UV-A-induced events.