Alopecia can be classified into many groups, depending on its origin and manifestations, but the most common form is genetic hair loss called androgenetic alopecia. This type of alopecia is caused by the action of male hormones or androgens on the hair follicle, causing its progressive miniaturization.
Also called common baldness, since it is responsible for 95% of cases, it mainly affects men and less frequently women and can occur from a very early age (around 18 years).
Other common forms of alopecia are alopecia areata, in which hair loss is not permanent and is commonly limited to a certain area; alopecia universalis, which is the extensive form of alopecia areata; and scarring alopecia, which is caused by destruction of the hair follicle and is therefore irreversible.
There are many varieties of less frequent alopecia that can be caused by genetic causes, medications, skin infections, trauma, nutritional deficiencies and certain skin or general diseases.