Hair Loss – Baldness

Baldness involves the state of lacking hair where it often grows, especially on the head. The most common form of baldness is a progressive hair thinning condition called androgenic alopecia or “male pattern baldness” that occurs in adult male humans and other species. The amount and patterns of baldness can vary greatly; it ranges from male and female pattern alopecia (androgenic alopecia, also called androgenetic alopecia or alopecia androgenetica), alopecia areata, which involves the loss of some of the hair from the head, and alopecia totalis, which involves the loss of all head hair, to the most extreme form, alopecia universalis, which involves the loss of all hair from the head and the body.

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Hair Loss – Background, cause and incidence

The average human head has about 100,000 hair follicles. Each follicle will grow an average of about 20 individual hairs in a person’s lifetime. Average hair loss is about 100 strands a day.

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 57% of women and 73.5% of men aged 80 and over. According to Medem Medical Library’s website, male pattern baldness affects roughly 40 million men in the United States. Approximately 25 percent of men begin balding by age 30; two-thirds begin balding by age 60.

Male pattern is characterized by hair receding from the lateral sides of the forehead, known as “receding hairline”. Receding hairlines are usually seen in males above the ages of 25 but can be seen as early as mid-teens.

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 hair on the head as well as the prostate.

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-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” (see ‘baldness folklore’ below)

There are several other kinds of baldness:

• Traction alopeciais 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 pullingand 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.
• 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 deficiencyis 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 mycotic infections can cause massive hair loss.
• Alopecia areatais 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 cicatricialalopecia (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).
• Hypothyroidismcan 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.

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Hair Loss – Evolutionary theories of male pattern baldness

There is no consensus regarding the details of the evolution of male pattern baldness. A number of other primate species also experience hair loss following puberty, and some primate species use an enlarged forehead, created both anatomically and through strategies such as frontal balding, to convey increased status and maturity. The assertion that MPB is intended to convey a social message is supported by the fact that the distribution of androgen receptors in the scalp differs between men and women, and older women or women with high androgen levels often exhibit diffuse thinning of hair as opposed to male pattern baldness.

One theory, advanced by Muscarella and Cunningham, suggests baldness evolved in males through sexual selection as an enhanced signal of aging and social maturity, whereby aggression and risk-taking decrease and nurturing behaviours increase. This may have conveyed a male with enhanced social status but reduced physical threat, which could enhance ability to secure reproductive partners and raise offspring to adulthood.

In a study by hector by Muscarella and Cunnhingham, males and females viewed 6 male models with different levels of facial hair (beard and mustache or clean) and cranial hair (full head of hair, receding and bald). Participants rated each combination on 32 adjectives related to social perceptions. Males with facial hair and those with bald or receding hair were rated as being older than those who were clean-shaven or had a full head of hair. Beards and a full head of hair were seen as being more aggressive and less socially mature, and baldness was associated with more social maturity. A review of social perceptions of male pattern baldness has been provided by Henss (2001) .

Other evolutionary hypotheses include genetic linkage to beneficial traits unrelated to hair loss and genetic drift.

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