While there are any number of underlying causes for hair loss that affect women, the vast majority of cases can be attributed to one of two conditions. Sometimes these two conditions overlap with both of them contributing to an individual's noticeable hair loss.
The most common cause is called female pattern hair loss (FPHL). It is a chronic, progressive hair loss that can start at any age and presents as progressive thinning of the hair, particularly at the top and front of the scalp. The cause is not entirely clear but is believed to be multifactorial, including possibly genetic predisposition and hormonal factors. The earlier medication is begun the better likelihood of slowing progression and seeing regrowth.
The other common hair loss condition is called telogen effluvium (TE). The condition is characterized by an increase in the amount of shedding that one normally experiences. The condition represents the early release of hairs that are in the resting phase of the hair growth cycle. It's typically brought on by some sort of trigger event.