Biopsy: Piece of tissue cut out for microscopic examination
Bonding: A term used to describe the simple act of gluing a hairpiece onto the scalp.
Catagen: The intermittent stage between the growing (anagen) and resting (telogen) phases of the hair's growth cycle.
Chemotherapy: Chemical treatment, usually of cancers, using drugs that have high levels of toxicity, frequently causing temporary alopecia.
Club Hair: A hair that has stopped growing or is no longer in the anagen phase. It is anchored to the skin with its "club-like" root, but will eventually be pushed out and replaced by a growing hair.
Cobblestoning: "Plugs" that have not healed flush with the skin and therefore have left the scalp lumpy. "Plugs" seldom heal flush with the skin. Cobblestoning occurs in almost all "plug" procedures.
Cortex: The layer of the hair shaft that surrounds the medulla and is filled with keratin fibers. The main structural part of the hair fiber that accounts for most of its size and strength.
Crown: The highest part of the head.
Cuticle: The outer surface of hair, composed of overlapping scales made of colorless keratin protein. It gives hair luster and shine and also provides some of its strength.
Dermal Papilla: The dermal papilla is situated at the base of the hair follicle. The dermal papilla contains nerves and blood vessels, which supply glucose for energy and amino acids to make keratin. This structure is extremely important in the regulation of hair growth since it has receptors for both androgens and hair-promoting agents.
Dermis: One of the two layers of cells that form skin. Specifically, it is the innermost layer.
Dihydrotestosterone (DHT): Male hormone thought to be the main cause for the miniaturization of the hair follicle and for hair loss. DHT is formed when the male hormone testosterone interacts with the enzyme 5-alpha reductase.
Donor Site: Area where pieces of hair-bearing skin are taken from during a hair transplant.
Double Blind Study: A scientific study where neither the subjects nor the researchers know who specifically is receiving the drug of treatment under study.