Alopecia is a condition that causes hair loss or baldness. Alopecia can be classified into numerous categories, including:

1. Alopecia Areata: This is an autoimmune condition that causes erratic hair loss. Hair usually falls out in little spots around the size of a quarter. For most people, hair loss is limited to a few spots, however it can be severe in other situations.

2. Androgenetic Alopecia: The most prevalent type of hair loss that affects both men and women. This disorder is also known as male-pattern baldness in men. Hair falls out in a predictable pattern, commencing above both temples and ending at the crown of the head.

This type of alopecia appears in women as gradual hair loss at the portion line followed by spreading diffuse hair loss from the top of the head.

3. Alopecia Universalis: Alopecia universalis is a kind of alopecia that results in total body hair loss, including eyelashes and eyebrows.

4. Traction Alopecia: This condition results from pushing hair into tight hairstyles, which causes it to break and come loose, resulting in hair loss.

5. Telogen Effluvium: This is transient scalp-wide hair thinning that results from modifications to the hair growth cycle.