The Effect of Plucking Hairs during Different Phases of the Follicular Cycle.

HAIR growth is intermittent; periods of activity when the follicle is producing the hair alternating with periods of rest when the dead hair is retained. In the rat, hair growth occurs in a series of waves which start ventrally and pass over the flanks to the back (Dry, 1926; Butcher, 1934; Johnson, 1958). It has long been known (Collins, 1918; David, 1934) that if hairs are pulled out of resting follicles activity is induced. To explain this phenomenon, Chase (1955) put forward the view that an inhibitor accumulates in the hair follicle during active growth and is dissipated during the resting stage. Plucking during the resting stage removes this inhibitor along with the club hair, so that activity recommences. Preliminary observations on rats with plucked follicles indicated that the response to plucking varied at different stages of the hair cycle. A detailed study seemed desirable, therefore, in order to test more closely than hitherto the validity of the inhibitor hypothesis.