Why do cats lick each other?

In a multicat household, it's common to see one cat licking another. When some people see this behavior, known as allogrooming ("allo" means "another individual"), they assume it's a sign of friendship.

But is that really the case? Are there hidden, more complex reasons for why cats lick each other?

While research into allogrooming is ongoing, scientists have suggested different explanations for why cats lick each other, including some social reasons and some more practical ones.

The historical view, based on observations of free-roaming-cat colonies, was that allogrooming is a sign of affection and helps cats create and maintain bonds with other cats in their social group, perhaps by creating a shared group smell .

But a 1998 study of 25 cats living together in an indoor-outdoor enclosure poked holes in this theory. The study found that aggressive behavior showed up in about 35% of allogrooming sessions, which suggested that allogrooming might not be about friendship. Instead, the authors proposed, it may help to defuse a tense situation in a confined space, where an actual fight would be too risky.

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To investigate, Morgane Van Belle , a cat behavior scientist at Ghent University in Belgium, and her colleagues analyzed videos of allogrooming from 53 two-cat homes. They concluded that allogrooming may have different social functions , depending on the situation.

The team noticed that the cats sometimes licked each other while huddling together and copying one another's body postures. In these moments, allogrooming probably helps strengthen social bonds, the researchers proposed. Most licking was directed toward the ears; this may help cats relax because the skin there is rich in sensory nerve endings, Van Belle said. Allogrooming produces a relaxing effect in other animals too. For example, it lowers the heart rate in horses and triggers the release of feel-good hormones in monkeys .