Alopecia universalis: Absence of all of the hair, not only on the scalp, but also on the entire body. Affected individuals are born without eyebrows and eyelashes and never develop axillary or pubic hair. There are hair follicles but they are devoid of hair. The disorder is inherited as an autosomal recessive trait. It is caused by a mutation in a gene dubbed HR in chromosome band 8p21.2 that is the human homolog of the mouse "hairless" gene -- the human version of the gene in the mouse that is responsible for hairless mice.

Alopecia universalis is one type of alopecia (alopecia means baldness). Other forms of alopecia include:

• Alopecia capitis totalis: Complete baldness of the scalp, but normal body hair.
• Alopecia areata: Patchy areas of baldness resulting from an autoimmune disorder with a probable genetic predisposition.
• Hair loss as a result of chemotherapy, the resultant hair loss usually being temporary.
• Hair loss as a result of radiation therapy administered to the head, the hair loss usually being permanent, due to irreversible damage to the hair follicles.
• Bald pate: Common male-pattern baldness localized to the front and top of the head, due to genetic (hereditary) factors.