My cat has a bald belly!

You need to take your cat to a vet. He could have any number of things. The most common reason for this is stress or food allergy. Try putting him on a food with only one ingredient, like Wellness Chicken. Try it for about a month to see if it helps. Has anything changed in the household that could stress him? I think the first step should be a vet check.

It might not be a medical condition. I have had cats that will pull the hair from their abdomen during the hot weather so that they stay cool. It's a bit un-nerving but the hair grows back. Watch your cat and see if he is doing this...other wise, it could be an allergic reaction. Is the weather warm? If so, it could very well be that he is pulling out the hair to cool off. (It sounds so weird, but I've had three cats that do it every spring and they are "hairless" through until late October/early November.

It might be that he's under some kind of stress. They can try to destress by grooming to excess and this can remove hair and leave a bald spot. It will grow back though.