Let's get to the bottom of this bizarre behavior.
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dog sniffing another dog's buttt on the beach with what the fluff logo
Credit: Daniel Rodriguez / Adobe Stock

Nothing can bring on a blush quite like watching your well-mannered pup suddenly transform into a dogged derriere detective, thrusting his nose into the nether regions of both pets and people. But why do dogs smell butts? Is there a reason?

According to Melissa McMath Hatfield, MS, CBCC-KA, CDBC, owner of Loving Dogs in Fayetteville, Ark., there are perfectly good reasons why your dog is a crotch examiner and butt sniffer (we mean this term in the kindest way possible). And better yet, there are ways you can gently redirect this behavior, when necessary.

Why Do Dogs Smell Each Other's Butts?

Dogs sniffing each other's bums is often described as the handshake of the canine world. "If you observe a normal meet and greet between dogs," Hatfield explains, "one will sniff the other's back end, and then they will switch positions and reverse the gesture. This ritual generally takes about three seconds, and it's considered to be a polite greeting."

But Hatfield says there's more to this greeting than meets the eye because dogs aren't just saying hello with their noses—they're gathering vital information with them thanks to their superhero-like smelling abilities.

"While human brains are dominated by the visual cortex," Hatfield says, "dog brains are dominated by the olfactory cortex, making their sense of smell the most powerful sense. Dogs have as many as 300 million olfactory receptors in their noses compared with approximately six million in humans."

As a result, it's been estimated that a dog's sense of smell is 10,000 to 100,000 times more acute than our own. Dog cognition researcher Alexandra Horowitz puts their abilities into more concrete terms, writing that a pup's snout could detect a teaspoon of sugar in two Olympic-sized pools worth of water.

So when a dog's super sniffer comes in contact with the unique and potent scent released by another dog's anal glands (two small sacs located inside the rectum), a fascinating amount of communication occurs. Hatfield says that by simply sniffing another dog's rear end, your dog can download details about his companion's health, sex, diet, social status, and, importantly, their mood.

"Dogs can smell adrenaline and pheromones," Hatfield says, "which can help them determine whether their companion is a friend or foe and whether they should fight, flee, or play." And because dogs are so good at remembering scents, they can use their snouts to ascertain whether they've met this bottom—er, dog—before.

Why Do Dogs Sniff Humans' Private Areas, and How Can I Redirect the Behavior?

Unfortunately, dogs don't limit their sensitive sniffers to members of their own species. They often "greet" you and your human guests the same way and for much the same reason: To gather important information.

"A quick sniff is all the dog needs," Hatfield says. "Otherwise, he's being rude, overbearing, or just plain nosey." (Pun intended.) But how can you gently curb a dog's privates investigation work? Elementary cues, my dear Watson.

Hatfield advises redirecting your dog from his human crotch examination by employing one of the cues he knows. "This will allow the moment to pass and will engage your dog in something else more appropriate."

While just about any trick will do, Hatfield offers the following basic cues as helpful diversions:

And if you need a diversion to help your friend/neighbor/coworker forget that your dog's snout was just in their crotch, why not spout off some of your newly acquired trivia regarding canine sniffing abilities?

Should I Let My Dog Sniff Other Dogs' Butts?

"It's perfectly acceptable to let your dog sniff another dog's private parts and vice versa," Hatfield says. "But keep in mind that a well-socialized, polite greeting generally lasts between three to five seconds. If the sniffing lasts any longer than this, consider it a red flag and separate the dogs."

Other signs that the sniff is about to turn into a tiff include low growling, raised hair, and one dog putting his head over the neck of the other dog.

A dog who doesn't want to be sniffed may also sit down in an effort to block the one-way communication from occurring. If you notice that your dog is trying to sniff a pup who would rather be left alone, you can employ the same redirection tactics outlined above to engage them in a more appropriate pursuit.