Human Hair

Head hair are grown on the head and is the most noticeable part of human hair, which can grow longer than on most mammals and is more dense than most hair found elsewhere on the body. The average human head has about 100,000 hair follicles. Its absence is termed alopecia, commonly known as baldness. Anthropologists speculate that the functional significance of long head hair may be adornment, a byproduct of secondary natural selection once other somatic hair had been lost. Another possibility is that long head hair is a result of Fisherian runaway sexual selection, where long lustrous hair is a visible marker for a healthy individual (with good nutrition, waist length hair—approximately 1 meter or 39 inches long—would take around 48 months, or about 4 years, to grow).
Each follicle can grow about 20 individual hairs in a person's lifetime. Average hair loss is about 100 strands a day.
The average human scalp measures approximately 120 square inches (770 cm²)

Psychological Implications

The psychological implications for individuals experiencing hair loss vary widely. Some people adapt to the change very well, others have severe problems relating to anxiety, depression, social phobia, and in some cases, problems with identity change. Retired NASA Astronaut Story Musgrave.Alopecia induced by cancer chemotherapy has been reported to cause changes in self-concept and body image. Body image does not return to the previous state after regrowth of hair for a majority of patients. In such cases, patients have difficulties expressing their feelings (what is called alexithymia) and may be more prone to avoiding family conflicts. Family therapy can help families to cope with these psychological problems if they arise.
Psychological problems due to baldness, if present, are typically most severe at the onset of symptoms.

Some balding men may feel proud of their baldness, feeling a kindred relationship with famous charismatic bald film actors such as Yul Brynner, Vin Diesel, Michael Chiklis, Telly Savalas, Ben Kingsley, Patrick Stewart or Bruce Willis; or politicians such as Ed Koch and James Carville; or sportsmen such as wrestler Stone Cold Steve Austin, footballer Zinedine Zidane or tennis star Andre Agassi. Much of these celebrities' perceived masculinity and handsomeness derives from their most obvious distinguishing feature. Baldness has, in recent years, in any case become less of a (supposed) liability due to an increasing fashionable prevalence of very short, or even completely shaven, hair among men, at least in western countries. This is not yet true for women, as there are few female celebrities who are bald by choice, chemotherapy or genetics/environment.

Many companies have built a successful business selling products that reverse baldness, by allegedly regrowing hair, transplanting hair or selling hairpieces. There is very little evidence that any of those which claim hair regrowth actually work.