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Chronic UVA Induces Photodamage

Chronic skin exposure to predominantly long-wave ultraviolet light (UVA) can occur in persons who work in cars or near bright windows or who use UVB-absorbing sunscreens during sun exposure. It is known that repetitive high-level exposure to UVA induces photoaging, but the effect of chronic low-level exposure to UVA, as would be seen in the above settings, has not been systematically studied.

The authors of this study exposed volunteers to high-dose UVA, solar-simulated UV radiation (including UVA, UVB, and infrared), and low-dose UVA (the same amount of UVA as in the solar-simulated UV regimen) at separate sites of previously non-sun-exposed skin. The 12 volunteers were irradiated twice per week for 24 weeks. Histologic evaluation of biopsies from the three sites of irradiation and from a control site was performed at 12, 24, and 36 weeks.

All three regimens of UV exposure produced thickening of the stratum corneum that was evident at 12 weeks, and partially persistent at 36 weeks, compared with the control site. Similarly, all produced vascular dilatation and a perivascular inflammatory response beginning at 12 weeks and continuing after irradiation was stopped. Finally, irradiation with both high- and low-dose UVA led to reductions in the content of dermal elastic tissue in the exposed skin.

Comment: These results provide good evidence that chronic exposure to UVA may lead to the histologic correlates of clinical photodamage and photoaging. Previous work has established UVB as the major mediator of photodamage. However, tanning in UVA tanning parlors, excessive exposure to UVA by sun worshipers using only UVB-absorbing sunscreens, and exposure to UVA through windows may cause photodamage in people who assumed they were protected. These results suggest that these people may benefit greatly from the use of sunscreens that absorb both UVA and UVB.

— PA Bleicher

Published in Journal Watch Dermatology February 1, 1996

Citation(s):

Lowe NJ et al. Low doses of repetitive ultraviolet A induce morphologic changes in human skin. J Invest Dermatol 1995 105 739-743.

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