General shedding and thinning of the hair. It usually occurs a few months after a shock to the system, such as extreme stress, fever, childbirth, sudden weight loss, an operation or as a reaction to medication. The hair loss is usually temporary.
Hair gradually thins, often from the top of the head. It usually gets more noticeable after the menopause and tends to run in families.
Affects mostly teenagers and young adults. Hair loss is patchy and linked to a problem with the immune system. The hair follicles are not permanently damaged, and in many cases hair grows back in a few months.
Complete loss of hair on the head. Regrowth is unlikely. Alopecia universalis Total loss of head and body hair.
Article sourced via: http://www.nhs.uk/Livewell/hairloss/Pages/Womenandhairloss.aspx