Alopecia

This is a condition where the immune system attacks the hair follicles resulting in hair loss. It is most common on the scalp but it can affect other areas of the body. There are different types of alopecia:
Alopecia areata, also known as spot baldness, in which hair is lost from some or all areas of the body. Often, it results in a few bald spots on the scalp.
In a few cases, all the hair on the scalp is lost (alopecia totalis), or all body hair is lost (alopecia universalis), and loss can be permanent.