5-Alpha Reductase - is the enzyme that converts the male hormone testosterone into dihydrotestosterone (DHT). This hormone is believed to cause some hair follicles on the head to shrink, thus producing finer and finer hairs with each growth phase. Eventually, no hair is produced. Much hair loss research has focused on reducing the levels of 5-alpha reductase to prevent the conversion of testosterone.

Alopecia - is the medical term for baldness or loss of hair. The term alopecia refers to complete or partial hair loss resulting from genetics, illness, injury or other causes.

Alopecia areata - is a disorder characterized by round, completely bald patches. The cause is unknown but there is a family history in about 20% of all cases.

Alopecia totalis - is the complete loss of hair on the head. Alopecia totalis sometimes starts out as alopecia areata.

Alopecia universalis - is the complete loss of hair over the entire body, including all facial hair, eyelashes, eyebrows and pubic hair. It may start as alopecia areata and progress to universalis.

Anagen - this is the growth phase of the hair growth/rest cycle. It can last from one to seven years.

Androgenetic alopecia - the medical term used for male and female pattern baldness that is the result of a genetic predisposition. The person with androgenetic alopecia will produce high levels of DHT, which will have an adverse affect on hair follicles.

Androgens - the general term used for any male hormone.

Antiandrogens - block the effects of androgens in the body.

Bonding - is the process of attaching (gluing) a hairpiece to the head.

Catagen - is the short, transition phase between the growth (anagen) and resting (telogen) phases of the hair's cycles.

Cortex - is the hair's main structural part. It determines the hair's size and strength, as well as texture and color.

Cuticle - is the outer, scaly part of the hair.

Dermal papilla - situated at the base of the follicle, the dermal papilla contains nerves and blood vessels used to provide glucose and amino acids to the hair.

Dihydrotestosterone (DHT) - is the hormone thought to be responsible for the shrinking of hair follicles leading to hair loss. It's formed by the enzyme 5-alpha reductase's interaction with testosterone.

Donor site - is the area of the scalp from which hair follicle bearing skin is taken and then transplanted at the recipient site.

Finasteride is the drug sold as Propecia, which is approved as a treatment for hair loss. It's sold in tablet form for baldness, but was originally developed to treat benign and enlarged prostates. It is approved for men only because it is known to cause birth defects. Women should neither take nor handle finasteride if they are pregnant, or will become pregnant.

Follicle - the sheath below the scalp in which the hair grows.

Grafting - the transplanting of hair from the back of the head to a recipient site. Most forms of grafting are outdated and no longer in use.

Grafts - transplanted hair.

Keratin - the protein that makes up hair, fingernails and toenails.

Male pattern baldness - is the most common form of baldness affecting a large percentage of men. Genetics and hormones as well as age cause it. It's a progressive hair disorder that eventually leaves the familiar horseshoe shaped hair pattern on the head.

Minoxidil - is the name for the topical hair loss drug sold as Rogaine. It sold in concentrations from 2% to 5% and was the first FDA approved hair loss medication. Women as well as men use it.

Micrograft - is a hair graft containing 1 or 2 hairs.

Papilla - is the small are at the hair's root responsible for providing nutrients to the follicle.

Recipient site - is the area that donor hairs are transplanted to.

Saw palmetto - is a natural herb that has some effectiveness as an antiandrogen.

Scleroderma - a connective tissue and skin disease. Scleroderma can lead to hair loss in the areas of the scalp that are affected.

Telogen - this is the resting cycle for hair lasting approximately 3 months. At any one time about 85% of the hair on the head is growing and 15% is in the rest phase.

Testosterone - the male hormone responsible for the development of male characteristics. It conversion to DHT is thought to cause hair loss.

Traction alopecia - a condition of hair loss caused by stressful hairstyles that pull the hair tightly including braids, ponytails and other pulling styles.