Abdominal hair is thehair that grows on theabdomen of humans and non-humanmammals, in the region between thepubic area and thethorax (chest). The growth of abdominal hair follows the same pattern on nearly all mammals, vertically from the pubic area upwards and from the thorax downwards to thenavel. The abdominal hair of non-human mammals is part of thepelage, (hair orfur).
It connectspubic hair andchest hair.
Beforepuberty, the abdominal region of both males and females is covered with very finevellus hair. In response to rising levels ofandrogens (mainlydihydrotestosterone) during and after puberty, the skin of the abdomen begins to produce coarser, longer and more pigmented hair (terminal hair). This process primarily affects men. Initially, hair grows in a vertical line from the pubic area up to the navel and from the thorax down to the navel. The development of abdominal hair normally begins in the final stages of puberty. With some men, the abdominal hair will stay within a clearly defined vertical line, but in others, terminal hair will appear laterally as well as vertically, particularly in the area around the navel. This lateral spreading can continue into middle age.
Some women may develop a small line of hair from the pubic area up to the navel. Excessive abdominal hair on women, following the male pattern, is a type ofhirsutism.
Richard Zickler performed a 1997 study of photographs of the above patterns and their occurrence in 400 white men and 400 white women,[3] paying particular attention to the development of hair during puberty. In Zickler's study the horizontal pattern was most common in females with an incidence of about 80 percent. The acuminate pattern occurred in about 55 percent of males and occasionally in females. The disperse pattern occurred in about 19 percent of the males studied.[3]
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The following journal articles include sketches of different abdominal hair patterns and observed percentages of men exhibiting each pattern.