What to do if i have a birthmark on my bottom lip, is this rare?

Birthmark: Was it present at birth? Is it growing bigger? Uncommon but not rare.

See below.: Is it really a birthmark, or is it new? It is not uncommon to have a birthmark anywhere on the body. If it is new, though, you should have a dermatologist check it. If it's been there since birth but has changed, you should also have it checked. If it's been there since birth, but has not changed, you only need to have it checked if it bothers you cosmetically.