Can I use Retin a (Tretinoin) for my very dark underarms? (Photos)

My am India. The skin has kind of thick layer like consistency, looks disgusting. I have had this for as long as I can remember and I am sickened by site of it. I've had hair removal laser ne many years ago so I don't use a razor as I have no hair growt. There is no irritation or rashes or broken skin. Please tell me if I can use retin a? Is it safe for this area? Most importantly does it work as I don't want to be wasting money and time if it doesn't work? Photos are of both armpits.