Skin responds to biological rhythms.

• Position: Your Life - Epidermal and Sensory Research and Investigation Center (CERIES - Brief Article

Research carried out by the Epidermal and Sensory Research and Investigation Center (CERIES), Paris, France, confirms that several aspects of skin function vary during the course of a day. Over the years, researchers have discovered numerous biological rhythms, sleep and menstrual cycles being the most-obvious examples. Levels of certain hormones fluctuate markedly over 24 hours. Fluctuations that occur within this time frame are called circadian variations. Overlaying these circadian rhythms are biological functions that cycle over several hours, called ultradian rhythms.

"Experimental studies suggest that these variations may contribute to the expression of some symptoms in conditions such as allergic disorders and cancer, as well as have an influence on the metabolism of certain drugs," explains Erwin Tschachler, professor of dermatology, University of Vienna, Austria, and Scientific Director of CERIES. "We, however, were interested in the effects that these underlying changes may have on healthy skin."

Although several previous studies examined circadian variations in the skin, many of these were performed on the back or inside of the forearm. "Facial skin is not only more complex in structure than skin on the forearm, but the face is also one of the sites most exposed to the elements. Therefore, we believed that the changes in the face might differ from those in other parts of the body," indicates Isabelle Le Fur, head of the Skin Bioengineering Unit at CERIES.

To examine circadian variations in facial skin, the researchers enrolled eight healthy Caucasian women and then measured various features of skin on the face and forearm in a carefully controlled environment over a...