6 min read

Why Do Dogs Love Sniffing Butts?

It's a very important form of communication.

Nose-to-butt may seem like an odd way to say, “How do you do?” but it’s a far more practical greeting than a handshake — for dogs, at least.

Pet owners have long wondered why dogs sniff butts, but this mysterious behavior is not as strange as it may seem. There is no better way for a dog to get to know her fellow canine than by using the most powerful tool at her disposal: that cold, wet nose.

A dog’s nose contains nearly 300 million scent receptors, compared to a human’s 5 million. In addition, the part of a dog’s brain that processes smell is 40 times greater than ours. One quick sniff and a pup can learn an awful lot about her new friend (or enemy).

“Dogs gather a lot of information about the world around them from their noses,” Dr. Elizabeth Stelow, chief of animal behavior services at the University of California, Davis, told The Dodo. “So, when they meet, smelling is a great way to find out more about the other dog.”

Like a secret language, dogs can communicate through scent. Their powerful sense of smell helps them to interpret their surroundings and read different chemical messages left by other dogs.

“This is one reason most male (and some female) dogs spend much of their time on walks urine marking in different locations — they send signals about having been there,” Stelow said. “It’s also why they scratch the ground after defecating (they have scent glands on the bottoms of their feet).” The glands on the paws secrete pheromones, similar to the pair of scent glands on their butt, so when your dog scrapes the dirt, she is leaving olfactory clues for the next animal who happens to come along.   

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Pet owners concerned that their dog is picking up some unsavory scents when performing this intimate behavior can rest easy. Dogs possess the vomeronasal organ, also known as Jacobson's organ, a second olfactory system found in many reptiles, amphibians and animals. The Jacobson’s organ processes pheromones from other animals separately from odor molecules, and provides a direct channel to the brain for the deciphering of these chemical signals.

When your pup sniffs another dog’s behind, he is gaining important information about that dog’s identity and sex, such as whether the other dog is sexually intact and ready to mate, Stelow explained. “Depending on what they find, it may affect what they do next (play, show aggression, urine mark nearby, initiate courtship, walk away, etc.),” Stelow added.

The very act of sniffing can tell your dog a lot from a behavioral standpoint. When done appropriately, a well-performed sniff of the bottom can signal good social skills among the pup population, telling the other dog whether they are “behaviorally competent versus awkward,” Stelow noted.

If a dog is unwilling to sniff or be sniffed, this can be a clear sign that something is wrong. “A dog that won’t let another dog sniff it may be afraid of that dog (or all dogs); owners should watch for how comfortable their dog is about that interaction,” Stelow added.

This behavior may also occasionally happen to dog owners, though our pets cannot glean the same amount of knowledge about us with their nose. “I have had female owners tell me their dogs sniff them more at certain times in their cycles,” Stelow said. “We use fragrant detergents and body soaps; so we’re probably not generally as interesting to sniff.”

So next time you see that doggy yin-yang forming, know it’s just your dog doing a little detective work before making friends.