Why Are Dogs Lips Serrated? The Most Common Theories

No one knows with certainty why dog lips are serrated, but experts have made a few educated guesses over the years. Some of the common theories include: to protect the lips from the teeth, to get a tight grip on bones, to help clean the teeth, and to allow the mouth to open wide.

Why Dogs Have Serrated Lips

Below are some of the most commonly believed reasons why dogs evolved to have serrated lips. Although none of them have been proven, they make a lot of sense.

To Protect the Lips From the Teeth

One of the most common beliefs about dog lips is that they are serrated to move out of the way of the teeth, especially the canine teeth, which overlap when dogs’ mouths are closed.

It’s also important for the lips to stay out of the way when the dog is chewing on something like a bone or toy.

To Hold Things

Another theory is that dogs’ lips are serrated to make it easier to grasp objects, whether it be bones, toys, or when they carry their young.

Some people think that the serration allows dogs to use their lips in addition to their teeth when carrying fragile puppies.

However, it’s more likely that dogs can carry their young without harming them because dogs instinctively know how much pressure is enough to harm a puppy and how to apply less pressure.

Their mouths are, after all, their only real way to carry things, so they’re skilled in knowing how much pressure they need to exert for different objects.

To Clean the Teeth

A Professor of anatomy named Frederick Wood Jones hypothesized in a paper in 1918 that the serrations on dogs’ lips, along with other features of a dog’s mouth, are designed to clean the teeth.

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It sounds a little far-fetched, but if you think about it, many tartar-removing toys, such as Nylabones, have little nubs on them that remove tartar by rubbing against the teeth.

So maybe Dr. Jones was on to something after all.

To Increase Taste

Some people speculate that the lip serrations increase the surface area of the skin inside the mouth, allowing dogs to have a stronger sense of taste.

While it’s certainly possible that this is true in a way we don’t yet fully understand, it’s also true that dogs only have taste buds on their tongues, and not very many at that.

If taste buds were distributed around the entire mouth, it’d be more likely, but dogs rely much more heavily on smell than taste when interacting with their environment, so this theory doesn’t seem to have much merit.

To Allow the Mouth to Open Wide

Dogs’ mouths are designed very differently than ours, with much longer lips and much shorter cheeks.

One theory suggests that dogs have serrated lips to increase the length of the mouth when the mouth is open.

This (according to this theory) is why the lips look crumpled when they’re relaxed and the mouth is closed.

Freedom of Expression

People who don’t spend a lot of time around dogs don’t realize how expressive their faces are, but dog lovers will tell you it’s true.

One of the most expressive areas of a dog’s face is its mouth. It’s possible that the serrated lips somehow aid in the different lip shapes that dogs make to communicate and express their moods.

Leftover from Puppy Days

It’s very possible that serrated lips help in nursing, and just remain in adulthood even though they no longer serve a purpose.

It makes sense that a puppy would need to be able to get a good grip and make a tight seal when suckling, and the lip serration may help with this. This is especially true since dogs lack the large cheeks that humans use to aid in suction.

Evaporative Cooling

Dogs lose much of their body heat through panting, which is a natural form of evaporative cooling.

As moisture in the dog’s mouth and nasal cavity evaporates, it creates a cooling effect, keeping the dog from overheating on hot days.

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Some theorize that lip serration increases the available surface area for moisture to evaporate, increasing the cooling effect and cooling the dog off more efficiently.

More Fun Facts About Dog Lips

Why Are Dog Lips Black?

Dog lips are black due to high levels of melanin.

Not all dog lips are black, however. They’re sometimes grey or brown, depending on how much melanin is present.

Most experts agree that dog lips are dark in color because they don’t have hair, and are therefore exposed to the sun’s UV rays.

Melanin protects against sun damage like sunburn and skin cancer.

Do Dogs Smile?

Dogs don’t smile in the way that humans do, but they have 2 of their own versions:

Submissive smile: looks a lot like baring teeth, as the top lip retracts from a closed mouth to show the front teeth. This can be a nervous, submissive gesture and is often used when greeting an animal or person that they want to befriend but are unsure about

Happy smile: when a dog looks like he’s smiling in human terms, his mouth is relaxed and usually open, and the corners of the mouth go way up. Technically, the dog isn’t smiling, he’s just content, so the muscles of the mouth are completely relaxed and devoid of tension

Sense of Taste

Sense of taste is one of the few ways humans have dogs beat since ours is much stronger.

Humans have about 10,000 taste buds all over the top of the tongue. On the other hand, dogs only have about 1,700, and most of them are at the tip of the tongue.


Dogs have more teeth than humans do, with 42 once they reach adulthood, compared to humans’ 32.

Unless you’ve raised puppies, you might not be aware that dogs have baby teeth that they lose, just like humans. This is one reason why puppies are chewing on everything since they get teething pain just like human babies.

Cooling Through the Mouth

As mentioned earlier, the primary way dogs cool off is by panting. This creates a cooling effect when the moisture in the dog’s breath, mouth, and nasal passages evaporates.

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This effectively exchanges the hotter air from inside the dog’s body with cooler air, in much the same way that drinking a glass of ice water will cool you from the inside out.

Dogs sometimes do pant due to other reasons, though, so make sure you keep an eye on your dog if he’s panting excessively or pants regularly, even when it’s not hot.

Excessive panting can be a sign of:

  • anxiety
  • pain
  • difficulty breathing
  • high fever
  • excitement
  • reaction to medications
  • Cushing’s disease
  • heart disease

Most of the time, panting is no cause for alarm. But if it seems out of the ordinary, there might be something more going on than just heat.

There’s a Reason For Lip Serration – We Just Don’t Know What

Although no one knows why dog lips are serrated, it’s definitely an interesting thought experiment to try and figure it out. One thing’s for sure: evolution doesn’t make mistakes, so if dog lips are serrated, there’s probably a good reason for it, even if we don’t know what it is yet.

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