NEW YORK (Reuters Health) - Sun exposure may contribute to skin aging by blunting the skin's ability to produce collagen in response to estrogen, new research published in the Archives of Dermatology suggests.

In both natural skin aging and skin aging due to sun exposure, known as photo aging, the skin's production of the key structural protein collagen is reduced, while existing collagen in the skin is degraded, Dr. Gary J. Fisher and colleagues from the University of Michigan Medical School in Ann Arbor explain. The collagen content of women's skin is reduced after menopause, and investigations of the effects of topical estrogen replacement therapy on the skin have had mixed results.

In the current study, Fisher's group looked at the effects of applying moisturizing cream containing 0.01 percent, 0.1 percent, 1 percent, or 2.5 percent estradiol (estrogen), or moisturizing cream only, to the skin of healthy volunteers with sun-damaged skin. The study participants included 40 post-menopausal women and 30 men of about the same age. The average age of the overall group was 75 years old.

After 1 week, collagen production increased in the sun-protected hip skin of the women and to a lesser degree in the men. But in the photo-aged facial and forearm skin, estradiol application had no effect on collagen production in men or women.

Analysis of skin biopsies after 2 weeks of treatment demonstrated that the photo-aged skin of the face and forearm and non-photo aged skin of the hip had the same concentration of estrogen receptors. Levels of enzymes involved in estrogen production were also similar in sun-exposed and sun-protected skin. It appears that the effect of sun exposure on estrogen production was indirect and that estrogen penetrated both sun-exposed and sun-protected skin to the same degree.

"Our results suggest that alterations produced by long-term sun exposure hinder the ability of topical estradiol to stimulate collagen production in aged human skin," the researchers conclude.

Pfizer, Inc. helped fund the study, while one of the study's authors was a consultant for the drug company.

SOURCE: Archives of Dermatology, September 2008.

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