There are many types of alopecia (baldness or hair loss), each with a different cause. Alopecia may be localized to the front and top of the head, as in common male pattern baldness. It may be patchy, as in a condition called alopecia areata. Or it can involve the entire head, as in alopecia capitis totalis (also called alopecia totalis), and it can involve hair loss of the entire body, such as in alopecia universalis. Alopecia can be caused by medications, such as from chemotherapy for cancer. It can also be a result of an underlying disease, such as with an underactive thyroid gland (hypothyroidism) and systemic lupus erythematosus. Alopecia may have no symptoms other than the loss of hair, or it can be associated with itching and/or rash of the scalp.
The word alopecia comes from the Greek alopex for "fox." Foxes are less furry when afflicted with a skin disease (the "mange") that causes them to lose their hair. When a fancier word for "baldness" was sought, the mangy fox supplied it -- "alopecia" or, if you wish, "fox-mange" -- not a very positive image to associate with baldness!