What Causes A Skin Tag Inside The Buttocks?

I am asking for my husband because he will not go see a physician....... he operates machinery all day long and bounces around in the cab - he has what looks like a skin tag on the underside of his butt cheek. It started out small and got a little bigger, but seems to be remaining the same size for the past several months. It is the same color as his skin. Not hard. Doesn t appear to have puss inside. I m not sure what it is but it doesn t appear to be a cyst or a boil when compared to pictures online.