There are many conditions that contribute to or cause hair loss, but the most common cause, is androgenetic alopecia.

In androgenetic alopecia, hair on the top of the scalp is genetically programmed to thin and die when exposed to the hormone dihydrotestosterone (DHT), which is a breakdown of the natural occurring hormone testosterone. The hair on the sides and the back of the head is genetically programmed to resist the effects of DHT. Transplant surgeonDr.Rahul Goyal realize early on hair moved from the back of the scalp to the balding areas would grow indefinitely. This concept, called donor dominance, revolutionized the theory of surgical hair transplantation.