Baldness is the state of having no hair or lacking hair where it often grows, especially on the head. The most common form of baldness is androgenic alopecia or "male pattern baldness". This syndrome occurs in adult male ( and a few female ) humans and other species. The degree and pattern of baldness can vary greatly; it includes male and female pattern alopecia (androgenic alopecia). This syndrome is also called androgenetic alopecia or alopecia androgenetica. An older term is alopecia seborrheica, used primarily in Europe. Pattern balding should not be confused with alopecia areata, which involves patchy hair loss. Extreme forms of alopecia areata are Alopecia totalis, which involves the loss of all head hair, and the most extreme form, alopecia universalis, which involves the loss of all hair from the head and the body.

The incidence of pattern baldness varies from population to population based on genetic background. Environmental factors do not seem to affect this type of baldness greatly. One large scale study in Maryborough, Victoria, Australia showed the prevalence of mid-frontal hair loss increases with age and affects 73.5% of men and 57% of woman aged 80 and over. According to Medem Medical Library's website, male pattern baldness (MPB) affects roughly 40 million men in the United States. Approximately 25 percent of men begin balding by age 20; two-thirds begin balding by age 60. There is a 4 in 7 chance of getting the baldness gene.

Male pattern is characterized by hair receding from the lateral sides of the forehead, known as a "receding hairline". Receding hairlines are usually seen in males above the ages of 20 but can be seen as early as late teens as well.

An additional bald patch may develop on top (vertex). The trigger for this type of baldness (called androgenetic alopecia) is DHT, a powerful sex hormone, body, and facial hair growth promoter that can adversely affect the prostate as well as the hair located on the head.[1]

The mechanism by which DHT accomplishes this is not yet fully 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-VII.

It was previously believed that baldness was inherited from the maternal grandfather. While there is some basis for this belief, both parents contribute to their offspring's likelihood of hair loss. Most likely, inheritance is technically "autosomal dominant with mixed penetrance"[citation needed].

There are several other kinds of baldness:

Traction alopecia is most commonly found in people with ponytails or cornrows who pull on their hair with excessive force.

Trichotillomania is the loss of hair caused by compulsive pulling and bending of the hairs. It tends to occur more in children than in adults. In this condition the hairs are not absent from the scalp but are broken. Where they break near the scalp they cause typical, short, "exclamation mark" hairs.

Traumas such as chemotherapy, childbirth, major surgery, poisoning, and severe stress may cause a hair loss condition known as telogen effluvium.[2] Hair follicles in the growing phase are affected by chemotherapy while this treatment targets dividing cancer cells. Therefore, almost 90% of hairs fall out soon after chemotherapy starts.[3]

Worrisome hair loss often follows childbirth without causing actual baldness. In this situation, the hair is actually thicker during pregnancy due to increased circulating oestrogens. After the baby is born, the oestrogen levels fall back to normal pre-pregnancy levels and the additional hair foliage drops out. A similar situation occurs in women taking the fertility-stimulating drug clomiphene.

Iron deficiency is a common cause of thinning of the hair, though frank baldness is not usually seen.

Radiation to the scalp, as happens when radiotherapy is applied to the head for the treatment of certain cancers there, can cause baldness of the irradiated areas.

Some treatments used to cure mycotic infections can cause massive hair loss.[4]

Alopecia areata is an autoimmune disorder also known as "spot baldness" that can result in hair loss ranging from just one location (Alopecia areata monolocularis) to every hair on the entire body (Alopecia areata universalis).

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

Hypothyroidism can cause hair loss, typically frontal, and is particularly associated with thinning of the outer third of the eyebrows (syphilis also can cause loss of the outer third of the eyebrows)

Hyperthyroidism can also cause hair loss, which is parietal rather than frontal.

Temporary loss of hair can occur in areas where sebaceous cysts are present for considerable duration; normally one to several weeks in length.

Congenital triangular alopecia – It is a triangular, or oval in some cases, shaped patch of hair loss in the temple area of the scalp that occurs mostly in young children. The affected area mainly contains vellus hair follicles or no hair follicles at all, but it does not expand. Its causes are unknown and although it is a permanent condition, it does not have any other effect on the affected individuals.[5]

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