passive diffusion from the blood supplying the hair fullicle, as the hair follicle is surrounded by a dense capillary network
From sweat, sebum and from the secretion of apocrine glands (only for pubic and axillary hair). Sweat is secreted by eccrine glands on the surface of the body, and can be considered a vehicle for the excretion of drugs. Sebaceous and apocrine gland ducts exit directly into the tunnel of the hair follicle just below the surface of the skin, thus the hair shaft (except for beard hair) is in tight contact with these secretions until it emerges from the skin
because of its high surface-to-volume ratio, the hair may be easily contaminated by the external environment, by exposure to chemicals in aerosols and smoke or by direct contact with powders
directly from the skin to the zone of hair synthesis