Diseases of the hair and nails
Both hair and nails are composed of keratin and are derived principally from the epidermal layer. Each may be affected by the same type of disease process, e.g. lichen planus, or altered by conditions that affect primarily the epidermis.
DISORDERS OF HAIR GROWTH
The extent and distribution of body hair is largely determined genetically. At the time of puberty, terminal hair growth occurs in males on the beard