Despite all the warnings to avoid exposure to the sun and to wear sunscreen, scientists don't really know how the sun damages our skin. Now, they're a bit closer to the answer.
Two scientists recently discovered that sunlight triggers a harmful reaction when it strikes a molecule in our skin--ironically a molecule once thought to be "nature's sunscreen." The work suggests the science behind the sagging, leathery skin typical of long-term sun worshipers, and may also shed light on how ultraviolet light causes skin cancer.
"We studied a natural component of human skin exposed to ultraviolet light and uncovered a new chemical reaction that may contribute to aging [of the skin] and cancer," said Dr. John Simon, who led the study.
The research will appear in the September 1 issue of the Proceedings of the National Academy of Sciences. The work was conducted at the University of California, San Diego by Dr. John D. Simon (who is now at Duke University), and his graduate student Kerry Hanson (who is now a postdoctoral fellow at the University of Illinois at Urbana-Champaign).
The sun's harmful rays come in two flavors: ultraviolet A and ultraviolet B. Evidence mounts that ultraviolet A and B both play a role in causing skin cancer and photoaging, which is characterized by deep, premature wrinkles, thickened skin, and age spots.
Time, gravity, and heredity notwithstanding, "something like 90 percent of all the visible signs of aging are from ultra-violet sources," said Dr. Kerry Hanson. "Photoaging is not just a cosmetic effect. It destroys the integrity of your skin."
The focus of this study is the sun-sensitive molecule called trans-urocanic acid
(t-UA). Formed in the top layer of the skin, t-UA molecules cover our bodies,
acting like antennae for light. In the 1950s, urocanic acid was hailed as a
"natural sunscreen" because it absorbs ultraviolet B light. It was thus thought
to protect against damage by such rays, which can potentially
Contact: Alisa Machalek
NIH/National Institute of General Medical Sciences