How is alopecia classified?

Alopecia (hair loss) can be divided into:
1. disorders of the hair shaft and
2. all other forms of hair loss.

Abnormalities of the hair shaft can produce alopecia because the shafts are fragile and “break off.” The other forms of alopecia can be divided into cicatricial (scarring) and noncicatricial alopecia. In cicatricial alopecia, hair is lost permanently. Both cicatricial and noncicatricial alopecia can be divided into diffuse and patterned hair loss. In diffuse hair loss, hair thins evenly from all parts of the scalp, and discrete “bald spots” do not occur. In patterned alopecia, certain areas of the scalp are affected more than others.

Eudy G, Solomon AR: The histopathology of noncicatricial alopecia, Semin Cutan Med Surg 25:35–40, 2006. Sperling LC, Cowper SE: The histopathology of primary cicatricial alopecia, Semin Cutan Med Surg 25:41–50, 2006.