Our hair follicles are sensitive to androgens, a hormone that effects hair growth. For men, androgens determine masculine characteristics including body hair. During puberty, androgenic hair growth appears on both boys and girls, but is more noticeable on the former. Hair first appears on the face, arms, legs, chest and shoulders, and some boys become hairier than others.
According to research done in the 1960s, there are 15 different ways hair grows on the chest of white males, and some 25 variations of the patterns. Hair can grow between the pectorals or cover them completely, even growing down the torso and into the pubic area. The study did not look at the chest hair patterns of other ethnic groups.
Back hair usually develops when a man is already in his 20s, but some men develop it during puberty. While it might seem undesirable, back hair is completely normal.
In the era of the metrosexual, it's become in vogue to trim and sheer body hair. According to fashion writer Chris Rovny, removing excess body hair can help eliminate body odor. He says the thicker your hair, the more body heat you produce, and next thing you know, you're sweating up a storm and giving off a funky odor.
There are several techniques for removing body hair. The easiest is shaving, using either a razor or clippers. At a salon, you can get a wax, where hot oil is used to strip off the unwanted hair. But these solutions are temporary. If you want hair gone for good, you need either electrolysis or laser removal.
Within the gay community, there is a culture that embraces body hair as a sign of unfettered masculinity. "Bears" are gay men who allow hair to grow with wild abandon, bucking the manscaping trend.
Depending on your faith, trimming and shaving body hair can either be sanctioned or forbidden. In the Islamic faith, men may remove their armpit and pubic hairs. They are also allowed to grow in their beards. In India, hair removal depends on whether you are Hindu or Sikh. Hindu boys will shave their heads at age 4 in a religious ceremony. As adults, males shave their heads as a sign of respect when an elder dies. For devout Sikh men, cutting or shaving any body hair is taboo. Unshorn hair is considered one of the five "outer signs" of the Sikh faith. In order to achieve purity, Thai Buddhists will often shave their heads. This is a sign of casting off the material and everyday world.