Hair replacement surgery is normally safe when performed by a qualified, experienced physician. Still, individuals vary greatly in their physical reactions and healing abilities, and the outcome is never completely predictable.

Consult with a qualified healthcare professional before making any decisions about hair restoration surgeries or medications.

About 90% of the hair on most people's scalps is in a two to six-year growth (anagen) stage at any given time. The other 10% is in a two to three-month resting (telogen) phase, after which time it is shed. Most people shed 50 to 150 hairs a day. Once a hair is shed, the growth stage begins again as a new hair from the same follicle replaces the shed hair. New hair grows at a rate of approximately one-half inch each month.

Hair loss may lead to baldness when the rate of shedding exceeds the rate of regrowth, when new hair is thinner than the hair shed, or when hair comes out in patches. Based on scientific evidence, hair loss does not result from poor circulation to the scalp, dandruff, or excessive hat wearing.

Pattern baldness (androgenetic alopecia), the most common type of alopecia, affects roughly one-third of men and women. It is genetic and usually permanent. Hair loss may occur as early the teen years in men, with balding typically characterized by hair loss that begins at the temples and crown. The result may be partial or complete baldness. Women with androgenetic alopecia usually have hair loss limited to thinning at the front, sides or crown. Complete baldness rarely occurs in women. With alopecia areata, baldness usually occurs in small, round, smooth patches. A person may lose only scalp hair or may lose body hair as well; this type of hair loss may be temporary.

Hair loss in all individuals is in part determined by heredity. A person's sensitivity to DHT (dihydrotestosterone), the hormone that shortens the hair life cycle, is genetically determined. DHT is believed to shorten the growth, or anagen, phase of the hair cycle, causing miniaturisation (shrinking) of the follicles, and producing progressively finer hairs. The production of DHT is regulated by an enzyme called 5-alpha reductase (5AR).

In men, the loss starts at puberty and continues with age due to the production of dihydrotestosterone (DHT), the active form of testosterone. The individual hairs become smaller, thinner, and less pigmented. The hair's growth cycle, usually four to six years, becomes shorter until it stops completely. Men see frontal recession and crown (top) thinning.

Hair loss in women usually begins after menopause. The significant hormonal and metabolic changes that accompany this stage of life usually play a role. Women usually do not experience complete baldness. The causes of hair loss in women are complex and are due to both hormonal (DHT) and non-hormonal factors. The loss is more diffuse and involves the back, sides, and top of the scalp with preservation of the frontal hairline. In women, medications to promote hair growth release anti-androgens.

Hair loss during pregnancy is uncommon, but occurs sometimes due to a vitamin or mineral deficiency or hormonal changes. Pregnancy-related hair loss most often occurs several months after delivery. During pregnancy, an increased percentage of hairs are in a growing phase and normal shedding of hair declines. After a woman gives birth, a large number of follicles shed hair at once. Although unsettling, this hair loss is temporary. Hair typically returns to its normal fullness and growth cycle within a few months. Individuals who experience hair loss in patches should consult their doctor.

Other common causes include illness, nutritional deficiencies, stress, medications, injury, high fever, scalp infection, harsh hair-care products, and some hair-styling practices. Cancer treatments, such as chemotherapy and radiation, also may cause hair loss. Some individuals may want hair restoration because of trichotillomania, a condition of compulsive hair pulling.

Several drugs have been approved by the Food and Drug Administration as safe and effective for treatment of hair loss.