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 primate species. The severity and
nature of baldness can vary greatly; it ranges from male and female pattern
alopecia (androgenetic alopecia, also called androgenic 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. Treatment for alopecia has limited success. The
more hair lost, the less successful the treatment will be.
Background, cause and incidence
The most noticeable part of human hair is the hair on the head, more prominent
in some than others, which is more dense than most hair found elsewhere on the
body. The average human head has about 100,000 hair follicles.[1] Each follicle
can grow about 20 individual hairs in a person's lifetime.[1] Average normal
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, in central 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.
Male pattern baldness 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 androgenetic alopecia) is DHT, a powerful sex hormone that adversely
affects the hair and prostate.[2]
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.
It was previously believed that baldness was inherited from a person's 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 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[citation needed].
Traumas such as chemotherapy, childbirth, major surgery, poisoning, and severe
stress may cause a hair loss condition known as telogen effluvium.[3]
Some 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, especially thinning of the outer third of
the eyebrows
Temporary loss of hair can occur in areas where sebaceous cysts are present for
considerable duration; normally one to several weeks in length.
Etymology
The term alopecia (al-oh-PEE-she-uh) is formed from the Greek αλώπηξ (alopex),
meaning fox. The origin of this usage is because this animal sheds its coat
twice a year.
The term bald derives from the English word balde, which means "white, pale", or
Celtic ball, which means "white patch or blaze", such as on a horse's head.[5]
There is no consensus regarding the details of the evolution of male pattern
baldness. Most theories regard it as resulting from sexual selection. A number
of other primate species also experience hair loss following puberty, and some
primate species clearly 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.(1) 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 Muscarella and Cunnhingham, males and females viewed 6 male models
with different levels of facial hair (beard and moustache 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.
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