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The hair follicle is a complex structure which produces the hair fiber consisting of a cortex, medulla, and cuticle (Figures 19-1 and 19-2). Hair follicles demonstrate the unusual ability to completely regenerate themselves. Hair grows, falls out, and then regrows. In the normal human scalp, up to 90% of hair follicles are in the growth phase called anagen, 1% in the transition phase catagen, and up to 10% in telogen or the loss phase. The anagen phase lasts approximately 3 years, catagen 2 to 3 weeks, and telogen 3 months.1

Figure 19-1.

Pilosebaceous Unit (Reproduced with permission from Mescher AL, ed. Junqueira's Basic Histology: Text & Atlas. 12th ed. New York: McGraw-Hill; 2010. Figure 18-12A).

Figure 19-2.

Hair follicle and fiber. Scanning electron microscopic image demonstrating layers of the hair fiber including the medulla (M), cortex (CO), and cuticle (CU) within the hair follicle. Major components of the hair follicle including the inner root sheath (IRS) and external root sheath (ERS) with surrounding connective tissue sheath (CTS) blood vessel (BV) and collagen bundles (CB) are also demonstrated (Reproduced with permission from Kessel RG, Kardon RH. Tissues and Organs: A Text-Atlas of Scanning Electron Microscopy. 1979).

Hair disorders are broadly grouped into the following categories:

  • The nonscarring alopecias associated with hair cycle abnormalities.

  • The scarring or cicatricial alopecias associated with inflammation and injury to the stem cell region of the hair follicle.

Hair loss is common and can occur with a variety of medical conditions. The workup of a patient with a hair disorder starts with a thorough history and physical examination as outlined in Tables 19-1 and 19-2, respectively.

Table 19-1.

Questions for the patient presenting with the chief complaint of "hair loss."

Table 19-2.

Physical examination of the patient with a hair disorder and the chief complaint of "hair loss."

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