Hair loss is a trait which 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 human males and some 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, which is more dense than most hair found elsewhere on the body. The average human head has about 100,000 hair follicles. Each follicle can grow about 20 individual hairs in a person’s lifetime. Average normal hair loss is about 100 strands a day.
|
|
Incidence of pattern baldness varies from population to population based on diet and personal habits. One large scale study in Maryborough, in central Victoria 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 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.
|
|
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”.
|
|
