The term alopecia means an abnormal hair loss. Indeed, it is normal that a number of hair fall every day due to their life cycle. However, beyond about 100 hairs per day, the hair loss becomes abnormal.
There are several forms of alopecia, usually classified according to three criterias :
Its extent, that is to say either alopecia located on a part of the scalp or diffuse alopecia, manifested by a uniform hair loss on the cranial region
Its character acute or chronic
The cicatricial character or not.
The best known and most common type of alopecia is androgenetic alopecia (baldness), followed by alopecia areata.