Diagnostic value of exclamation mark hairs.

Exclamation mark (EM) hair can lead to the misdiagnosis of alopecia areata (AA) because it is widely considered as pathognomonic for AA. Typical EM hairs were also found in trichotillomania. EM hairs collected from 2 cases of trichotillomania and 9 cases of AA were compared under light microscopy. There were two sorts of EM hairs, one with frayed distal ends and the other with blunt distal ends. The majority (77.8%) of the EM hairs from AA had frayed distal ends, while the majority (82.2%) of that from trichotillomania had blunt distal ends. EM hairs, even with frayed distal ends, are not pathognomonic of AA.