How the Skin Can Tell Time

The mammalian central circadian pacemaker, which is located in the suprachiasmatic nucleus (SCN) of the hypothalamus, synchronizes and entrains clocks found in peripheral tissues. Skin harbors an active circadian clock that is under the influence of the central clock. This clock, which probably operates in most—perhaps all—types of skin cells, may influence the regulation of several circadian physiological phenomena, including cell proliferation.