Hypertrichosis is a medical term referring to a condition of excessive body hair. It can be generalized, symmetrically affecting most of the torso and limbs, or localized, affecting an area of skin. It may be mild or severe. In most cases, the term is used to refer to an above-average amount of normal body hair that is unwanted and is an aspect of human variability.

In medical practice, once generalized hypertrichosis has been distinguished from hirsutism, it is most often considered a variation of normal, primarily resulting from genetic factors.

Severe hypertrichosis is quite rare, almost certainly due to unknown genetic defects, and can result in excessive or animal-like hair on both face and body. Unfortunately, some of these people have been displayed in carnival sideshows with names such as "dog-boy" or the "bearded lady." Fedor Jeftichew and Annie Jones are well known examples.

In 1982, an American geneticist called Frank Greenberg of the Baylor College of Medicine discovered a Mexican family with a rare genetic mutation that causes fur like hair to grow all over their bodies. The family was segregated from Mexican society, they were forced to hide in their home in Loreto's town, and can only obtain work in the circus. In the Aceves family which is composed of 32 members...all have this disease. They live in a mountain town named Zacatecas.

This condition has sometimes been falsely referred to as "Wookism" or "Wookieeism," a stereotypical nod to the hairy creature known as a Wookiee from the world of Star Wars.

Severe hypertrichosis was used as the basis for the character of Tara in the movie Blood Moon (Canadian title) (Wolf Girl, American title)