Every strand of hair you can see is actually dead.

Hair is produced within the hair follicle, a tiny tunnel-like segment of the epidermis that extends into the dermis. At the base of the follicle is the hair bulb, where living cells divide every 23 to 72 hours, faster than any other cell in the body. As these new cells grow, they push older cells upward through the skin. During this upward journey, a process called keratinization occurs. The cells fill with keratin, lose their nuclei, and eventually die, forming the sturdy hair shaft we see. By the time the hair emerges from the scalp, it is a non-living structure composed of approximately 65% to 95% protein. Because the visible hair shaft lacks a blood supply and a nervous system, it cannot transmit pain signals or regenerate tissue. This biological reality was first detailed extensively in dermatological studies during the early 20th century. Research from institutions like the American Academy of Dermatology confirms that once the hair cuticle is compromised, chemical treatments or heat cannot truly 'heal' the strand. The only living part of the hair is the papilla, which contains the capillaries that nourish the growing cells. This is why systemic health and nutrition directly impact the quality of new hair growth but have no effect on the hair that has already surfaced. Understanding this cycle is vital for trichology, the scientific study of hair and scalp health.