There are numerous forms of hair loss (alopecia), which can affect hair anywhere on the body. All forms of alopecia differ in causation (etiology) and severity, which can only be diagnosed by a medical provider.
Alopecia can be subdivided into two main categories: non-scarring and scarring. The most common type of non-scarring hair loss is known as androgenic alopecia, or simply male and female pattern hair loss. Androgenic alopecia is a common type of hair loss, affecting approximately 50% of men and 15% of women. The main culprits behind androgenic hair loss are thought to be factors such as genetics and hormones, including DHT.
Telogen effluvium is an additional form of non-scarring alopecia that arises from a shift in one's natural hair growth cycle towards a cycle with a shorter anagen (growth) phase and longer telogen (shedding) phase. Telogen effluvium may result from different factors such as an underlying illness, improper nutrition, or certain medications.
Alopecia areata can affect hair all types of hair, from the hair on your head to the hair on your body. When it affects a specific portion of the body it is referred to as alopecia areata, but when it begins to affect an entire site (bald patches) it is referred to as alopecia totalis. Furthermore, when the whole body is affected it is called alopecia universalis. As of now the exact biological mechanisms behind alopecia areata are not fully understood but research indicates it is the result of autoimmunity.
Traumatic alopecia, similar to traction alopecia, results from repetitive tension placed on the hair shaft and follicle. More common in children it can result from hair pulling or hairstyles that exert strain on the hair for prolonged periods.
All the above are forms are classified as non-scarring, and comprise the majority of hair loss cases. Scarring hair loss is collectively known as cicatricial alopecia and composed of less common forms of hair loss. Although all differing in etiology all forms of cicatricial alopecia result in a hair follicle that is irreversibly destroyed and replaced by scar tissue.