Hair is composed of strong structural protein called keratin. This is the same kind of protein that makes up the nails and the outer layer of skin.

Below the surface of the skin is the hair root, which is enclosed within a hair follicle. At the base of the hair follicle is the dermal papilla. The dermal papilla is feed by the bloodstream which carries nourishment to produce new hair.

Causes of hair loss are varied, and the most frequent is Androgenetic Alopecia - accounts for 95% of all hair loss. It can affect both men and women although men experience a much greater degree of loss. In women Androgenetic Alopecia appears as diffuse hair loss occurring over most of the scalp. In men however the pattern of loss usually starts with a receding hairline which then advances to thin the top of the head.

When Androgenetic Alopecia (male pattern baldness) occurs, large active hair follicles in specific areas begin to change to smaller less active ones that shrink slightly with each new growth cycle.

Male pattern baldness is thought to occur in varying forms in about 66% of adult males at some point in their lives. It is characterized by hair receding from the lateral sides of the forehead, known as "receding hairline" or "receding brow." An additional bald patch may develop on top (vertex). The trigger for this type of baldness (called androgenic alopecia because it is caused by male hormones or androgens) is DHT, a powerful sex hormone.

The mechanism by which DHT accomplishes this is not yet understood. In genetically-prone scalps, DHT initiates a process of follicular miniaturization. Through the process of follicular miniaturization, hair shaft width is progressively decreased until scalp hair resembles fragile vellus hair or "peach fuzz" or else becomes non-existent. Onset of hair loss sometimes begins as early as end of puberty, and is mostly genetically determined. Male pattern baldness is classified on the Hamilton-Norwood scale I - VIII.

Female pattern baldness, in which the midline parting of the hair appears broadened, is less common. It is believed to result from a decrease in estrogen, a hormone that normally counteracts the balding effect of testosterone, which normally occurs in women's blood. Female pattern baldness is classified on the Ludwig scale I-III.

Traction alopecia is most commonly found in people with ponytails or cornrows who pull on their hair with excessive force. Wearing a hat shouldn't generally cause this, though it is a good idea to let your scalp breathe for 7 hours a day.

Traumas such as chemotherapy, childbirth, major surgery, poisoning, and severe stress may cause a hair loss condition known as telogen effluvium.

Some mycotic infections can cause massive hair loss.

Alopecia Areata - is thought to be an auto-immune disease of the hair, initially appearing as a rounded bare patch about an inch across. Alopecia Areata affects both men and women equally and is often experienced first in childhood. According to a survey taken in America one person in every hundred is likely to experience Alopecia Areata at sometime in their life.

Localized or diffuse hair loss may also occurs in cicatricial alopecia (lupus erythematosus, lichen plano pilaris, folliculitis decalvans, central centrifugal cicatricial alopecia, postmenopausal frontal fibrosing alopecia, etc.). Tumors and skin outgrowths also induce localized baldness (sebaceous nevus, basal cell carcinoma, squamous cell carcinoma).