Human hair: a unique physicochemical composite.

All hair is ethnic. Categorizing diverse hair types into 3 major groups-African, Asian, and Caucasian-makes it easier to recognize characteristics specific to each hair type, such as curliness, color, and cross-sectional parameters. All hair, however, regardless of its ethnic origin, exhibits common characteristics of morphology, chemical makeup, and molecular structure. This article provides a brief review of the salient elements of hair structure, chemistry, and the fundamental interplay that contributes to the properties of the hair fiber and its response to treatments.