Hair Loss or Baldness is 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.
Incidence of pattern baldness varies from population to population based on genetic background. One large scale study done in Australia revealed the prevalance of mid-frontal hair loss increases with age and affects 57% of women and 73% of men aged 80 year and older.
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 20 but can be seen as early as late teens as well.
There is no consensus regarding the details of the evolution of male pattern baldness. 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 men or women with high androgen levels often exhibit diffuse thinning of hair as opposed to male pattern baldness.