Biology of Hair

Hair, a shared feature of all mammals, plays an important role in environmental protection, sensory enhancement, temperature regulation, and debris removal. Human hair has been historically classified into three ethnic subgroups: Asian, African, and Caucasian. While these groupings are grossly unscientific and fail to recognize the complex phenotypic diversity of hair, they continue to persist in scientific literature due to ease of reader comprehension and challenges classifying hair. This chapter explores the anatomy of hair, hair follicle immune privilege, the hair cycle, hair pigmentation, the science of hair curl, and alternative ways to classify hair beyond ethnicity.