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The hair follicle is a complex structure which produces a hair fiber consisting of a cortex, medulla and cuticle (Figures 30-1, 30-2). 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 2–3 weeks and telogen 3 months.1

Figure 30-1.

Pilosebaceous unit. Reproduced with permission from McKinley M, O'Loughlin VD, Pennefather-O'Brien EE: Human Anatomy, 6th ed. New York, NY: McGraw Hill; 2021.

Figure 30-2.

Cross section of scalp skin with anagen hair follicles. Hematoxylin and eosin stain.

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 this chief complaint starts with a thorough history and physical examination as outlined in Tables 30-1 and 30-2, respectively.

Table 30-1.Questions for the patient presenting with the chief complaint of "hair loss." Ask about the following:

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Table 30-2. Physical examination of the patient with the chief complaint of "hair loss."

  • Closely examine the scalp.

  • Document:

    • Erythema

    • Scale

    • Folliculitis

    • Evidence of scarring

  • Look for new hair growth (fibers with tapered ends) or hair breakage.

  • Pull test.

  • Note body hair density and distribution.

  • Document any nail abnormalities.

  • Use scales – Ludwig, Hamilton/Norwood, SALT or Ferriman Gallwey.

The nonscarring hair disorders associated with abnormalities in the hair cycle include three very common hair disorders:

  • Androgenetic alopecia (with or without androgen excess)

  • Alopecia areata

  • Telogen effluvium

These nonscarring hair diseases are associated with changes to the anagen, or growing stage of the hair cycle.

The scarring alopecias are ...

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