Cats lick each other’s rear ends primarily to gather chemical information. The perianal area is packed with scent glands that broadcast a cat’s identity, sex, reproductive status, and health. What looks like an awkward (or gross) social interaction is actually one of the most information-rich exchanges in feline communication.
The Perianal Area Is an Identity Card
Cats have concentrated sebaceous glands in the perianal region that produce a complex cocktail of fatty acids, ketones, aldehydes, and alcohols. These chemical compounds encode surprisingly detailed information: individual identity, age, sex, reproductive status, social rank, and even which social group a cat belongs to. A 2023 study published in Scientific Reports found that the anal gland microbiome varies dramatically between individual cats, with bacteria like Corynebacterium, Bacteroides, and Lactobacillus present in different proportions. Since bacteria play a key role in producing odor compounds, each cat essentially carries a unique chemical fingerprint back there.
When one cat licks or sniffs another’s rear, it’s reading that fingerprint. The information gathered in a few seconds would be like you glancing at someone’s driver’s license, medical chart, and social media profile all at once.
How Cats Process What They Collect
You may have noticed a cat make a strange open-mouthed face after sniffing another cat’s rear, with the upper lip curled back and a slightly glazed expression. This is called the flehmen response, and it serves a specific purpose. Cats have a specialized sensory organ called the vomeronasal organ in the roof of the mouth. By curling the lip and holding the mouth open, a cat channels fluid-borne chemical signals from the tongue and nasal passages directly to this organ, which is tuned to detect pheromones and other social chemicals that the regular nose can’t fully process.
Research on cats confirms that the flehmen response is almost always preceded by direct nose-to-surface or tongue-to-surface contact with the scent material. The cat isn’t just smelling passively. It’s actively collecting a sample and routing it to its most sensitive analytical equipment.
It Starts With Mom
This behavior has deep roots in kittenhood. Newborn kittens physically cannot urinate or defecate on their own. The mother cat licks the perineal region to stimulate a reflex that triggers elimination. This isn’t optional grooming; without it, the kitten’s waste would build up dangerously. The mother then consumes the waste to keep the nest clean and free of odors that might attract predators.
This early experience creates a lifelong association between licking the rear area and social caregiving. Kittens learn toilet habits by observing the queen and following olfactory cues she leaves. As adults, the perianal region retains its significance as a site of intense chemical communication, even though the elimination-stimulation function is no longer needed.
Social Bonding and Hierarchy
Mutual grooming between cats (called allogrooming) generally focuses on the head and neck, which are the areas a cat can’t easily reach on its own. Licking the rear is less common as a pure grooming behavior but serves a distinct social function tied to scent exchange rather than fur maintenance.
Allogrooming in general reflects the social dynamics of a cat group in ways that might surprise you. Research on confined cat colonies found that higher-ranking cats groomed lower-ranking cats more often than the reverse. Groomers also showed more offensive behavior than the cats being groomed, and they often displayed aggression shortly after a grooming session. This suggests that grooming isn’t always a purely affectionate gesture. It can function as a way of managing tension and redirecting potential aggression when outright conflict would be too costly for both parties.
Interestingly, genetic relatedness didn’t affect how often cats groomed each other. Unrelated cats in the same group groomed just as frequently as siblings, which points to grooming being more about social negotiation than family bonding.
When Rear Licking Signals a Problem
There’s an important distinction between occasional social licking and one cat persistently licking another cat’s rear, or a cat obsessively licking its own. Cats will lick a specific area when it’s painful or itchy. Focused licking at the tail base often points to flea infestations, while licking centered on the anal area can indicate anal sac impaction, where the glands become packed with thick, pasty secretions that the cat can’t express naturally.
Cats with anal sac problems may also scoot along the floor, strain during bowel movements, or show discomfort when the base of the tail is touched. Parasites like tapeworms can cause similar rear-focused irritation. If another cat in the household is paying unusual attention to a housemate’s rear, it may be detecting the abnormal scent profile that comes with infection or impaction. Cats pick up on chemical changes that are invisible to us.
More generalized excessive licking, spreading across the back, belly, or legs, tends to point toward allergies (food or environmental) or, in some cases, compulsive behavior disorders. Cornell University veterinary researchers describe these cats as “fur mowers” because they lick patches of fur completely away. The location of the hair loss often provides the first clue about the underlying cause, from parasites in young cats to neurological conditions in older ones.
Why Your Cats Do It at Home
In a multi-cat household, brief rear-sniffing or licking when cats greet each other is completely normal. It’s the feline equivalent of a handshake: a quick information exchange that confirms identity and checks in on the other cat’s status. You’ll often see it when one cat returns home after a vet visit or time in a different room, because the returning cat smells unfamiliar and the resident cat needs to re-establish who it is.
Cats that live together and have a comfortable relationship may do this casually and briefly. If the behavior is one-sided, prolonged, or seems to cause distress in either cat, it’s worth paying attention. A cat that repeatedly resists having its rear area investigated may be in pain. And a cat that obsessively seeks out another cat’s rear may be responding to an unusual scent that signals illness or glandular issues in the other cat. Adding fiber to a cat’s diet can help maintain healthy anal gland function by increasing fecal bulk, which naturally compresses and empties the glands during bowel movements.