Hair loss with thinning can affect both men and women.
It leads to a progressive, localized and, in some cases, irreversible hair loss. There are several types of alopecia with thinning.

Homme souffrant d'une alopécie androgénétique

Androgenetic alopecia is the most common hair condition in men, but it also affects 20% of the female population.
Androgenetic alopecia is usually hereditary and leads to the progressive thinning of the hair on the top of the scalp. There are solutions to slow down or even stop this process, but the hair will disappear for good if left untreated. 
Learn more about androgenetic alopecia

Scarring alopecia is caused by the accidental destruction of hair follicles or major inflammation of hair tissue (for example: dermatosis, follicular lichen or discoid lupus erythematosus).
The hair follicle is damaged beyond repair and replaced by a smooth, shiny scar. Only surgical or cosmetic solutions can correct alopecia.
Learn more about scarring alopecia

Telogen effluvium with thinning disrupts the life cycle of the hair and leads to massive hair loss. This disruption can be caused by a stress episode, childbirth, anesthesia, illness or separation.
Telogen effluvium is a temporary condition. The hair that fell out will grow back immediately and there are no lasting consequences on the hair.
Learn more about telogen effluvium