He's anxious. He probably has separation anxiety too, some animals also do this because they are bored/depressed Dogs & cats alike are like humans than we want to believe. Think of a child who ***** it's thumb...& can do this until it is raw or the thumb blisters. The child does this for security purposes. So, an animal will lick it's fur, paws, etc until it's bald, or sore. Depression can set in when you may have changed jobs (shifts), travel more often, bring in another pet, or just aren't spending the time you used to with him/her. This could be triggering this behavior.
Anxiety - my cat used to have separation anxiety so bad that if I didn't come home when she felt I needed to be there, she would vomit. I got her a sister...& now she's fine. But, they can also show respond to this anxiety by licking constantly.
Last but not least....allergies. My mother's dogs have an allergy to grass & will lick themselves so much my mother has to give them chew bones to distract them. As always I would contact my vet to see what he/she thinks. I hope he feels better soon.
Hi and welcome,
This *could* be a reaction to the grains in the food (unless you're feeding grain-free), but I would start with the easiest change, which is changing the litter to a different brand. This is a common allergic reaction for some kitties. Try a scent-free one if you're using a scented one now.