Why is my cat obsessed with my armpit?
Because our armpits (and groin) are as close as humans get to the scent glands cats have on their heads which they mark us and other animals with as a sign of affection.
Why is my cat sucking my armpit?
It’s because your scent permeates whatever you’ve worn, and under the right circumstances, this can be comforting to your cat. Armpits are full of scent-producing apocrine glands that produce pheromones. It’s no wonder that your cat finds your underarms interesting and can’t resist giving yours a lick now and then.