Traumatic alopecia
Traumatic alopecia may also be caused by breakage of the hair shaft due to acquired structural defects of the hair occurring by traumatic hair-care practices. The most common defect is acquired trichorrhexis nodosa, which can develop at any age as brittle, short hairs that are easily broken. Microscopically, the distal ends of the hairs are frayed, resembling a broomstick. Other hairs may have nodules that resemble two broomsticks stuck together on microscopy. Acquired trichorrhexis nodosa most commonly occurs in blacks arising from trauma of combing tightly curled hairs or from excessive usage of hot combs, hairdryers, hair straighteners, or other chemicals. This disorder is self-limited, and normal hairs regrow when the source of damage is eliminated.
Other forms of deliberate and accidental physical, thermal, and chemical injury to the hair shaft and scalp can also cause alopecia. Examples include child abuse and pressure necrosis of the skin.
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