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.
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.
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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)
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