Do the birth control pills that improve girls' acne also help decrease their body hair?

Yes...read on.: The point of ocp's to prevent acne and unwanted hair growth is to decrease the circulating levels of testosterone in your body. Birth control pills decrease free testosterone by increasing liver production of a hormone that binds up testosterone. Unwanted hair that is already there won't likely improve, but new unwanted hair growth should be prevented. Acne should also decrease after 2-3 month.

Possibly: Excess facial or body hair (hirsuitism) in women is caused by over-stimulation of the hair follicles by testosterone. As dr. Finke correctly points out, oral contraceptives help in acne or hirsuitism by decreasing the level of free testosterone. This effect can be further enhanced by the addition of another anti-testosterone drug called spironolactone.

But...: Medical therapy to prevent new hair growth will not eliminate hair that is already present. Depending on the color and thickness of the hair these can be removed using lasers or electrolysis. There is also a prescription cream called vaniqa that can slow the rate of hair growth but does not actually remove it.