A cat licking a patch of fur off is usually told it is stressed. There is a study on exactly that assumption, and it did not hold up.
In 2006, twenty-one adult cats were referred to a specialist having already been given a presumptive diagnosis of psychogenic alopecia, which is the formal name for hair loss caused by stress licking. All twenty-one were worked up properly.
Sixteen of the twenty-one, which is 76 percent, turned out to have a medical cause of itching. Only two cats out of twenty-one had stress alone. Three more had both. An adverse food reaction was diagnosed in twelve of them. The authors' conclusion:
Results suggest that psychogenic alopecia is overdiagnosed in cats. Thorough diagnostic testing should be done before ascribing a behavioral cause to hair loss in cats.
A veterinary dermatologist writing for practitioners puts it more bluntly still, saying the evidence suggests psychogenic alopecia is widely overdiagnosed and may be the least common of the possible explanations for hair loss in a cat.
That does not mean stress licking is imaginary. The behavior guidelines do list increased grooming, and sometimes self-injury, among the signs of a distressed cat. It means it is the answer you arrive at last, after the others are ruled out, rather than the one you start with.
This is the fork the whole thing turns on, and no amount of looking at the bald patch answers it. A vet plucks a few hairs and looks at the ends under a microscope. Broken, blunt ends mean the cat is removing the hair itself. Normal tapered ends mean the hair is falling out on its own, which is a different list of causes entirely.
Self-inflicted is by far the more common of the two, especially when the thinning is spread over a wide area. The documented causes include fleas, lice, several kinds of mite, ringworm, bacterial and yeast infections, flea allergy, food allergy, atopic dermatitis, an overactive thyroid, and skin lymphoma.
Hair that genuinely falls out on its own has its own causes, including follicle infections, hair that sheds early after illness or stress on the body, and rarely a pattern associated with internal tumors.
A cat licking its belly bald may be telling you where the pain is. The 2025 consensus guidelines on feline bladder disease list this directly.
Non-urinary signs may include overgrooming of the abdomen, perineum and hindlimbs, indicating underlying pain
So a bald stripe along the belly or the inside of the back legs is worth mentioning to a vet even if the cat is using the litter box normally. The Merck manual makes the same general point, that excessive grooming and self-injury can follow from anything causing nerve pain or itching.
The opposite presentation matters too. A cat that has stopped grooming and looks scruffy, particularly along the back and the base of the tail where it has to twist to reach, can be a cat whose joints hurt. The acute pain guidelines note that eating and grooming are normal behaviors that disappear quickly in a cat that is in pain.