identified by an active growth period known as anagen, an intermediate period known as catagen, and a resting stage known as telogen.
In the anagen phase, which lasts from 2 to 8 years (2), the follicle reaches its maximum length, and there is a proliferation of the matrix cells. Anagen hair generally has a thick shaft, and in given segments its medulla is clearly visible. The proximal-most part of the bulb in anagen hair is deeply pigmented. The bulb gradually tapers and becomes lighter in color at and beyond the keratogenous zone of the follicle. Catagen hair, in its involutional form, differs from telogen (clubbed) hair in two ways: (1) its keratinized (proximal) part is darker than that of clubbed hair; and (2) its inner and outer root sheaths are better preserved (5). Unlike the anagen phase, the catagen phase is short, lasting from 2 to 4 weeks (2). Telogen hair, or clubbed hair, is easily recognized because it generally contains a thin shaft, which is transparent near the root and devoid of a medulla and kerato-genous zone. The telogen phase also is much shorter than the anagen phase, lasting from 2 to 4 months (2). The normal anagen/telogen ratio is 9:1.
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