Armpit hair grows so fast and much faster than other hair because armpit hair is not rooted in eccrine sweat glands, which primarily control temperature.
That makes the armpit hair grow faster than other places on your body.
Your other hair is rooted in eccrine sweat glands, which makes the other parts of your bodies hair grow slower.
Also your armpits have more hair follicles than other body parts that grow hair so that's another reason armpit hair grows faster.
It's normal for armpit hair to grow back faster than other hair.
Armpit hair grows around 50 percent faster than other hair including leg hair, facial hair and head hair.
You could get rid of armpit hair nearly permanently or even permanently using laser hair removal surgery.