Dogs have long tongues primarily because they rely on them to cool down. Unlike humans, dogs can’t sweat through most of their skin, so their tongue acts as their main cooling system. But temperature regulation is only part of the story. A dog’s tongue is also a drinking tool, a grooming instrument, and a social communication device, and each of these jobs benefits from extra length and flexibility.
Cooling Down Without Sweat Glands
The single biggest reason dogs evolved long tongues is thermoregulation. Dogs have sweat glands only on their paw pads, which aren’t nearly enough to cool a warm body. Instead, they pant, and that’s where the tongue becomes essential. When a dog pants, moisture evaporates from the tongue’s surface, the nasal passages, and the lining of the lungs. Air flowing over these wet tissues carries heat away from the body.
A longer tongue means more surface area for evaporation, which means more efficient cooling. Research on lingual blood flow shows just how dramatically this system ramps up. When a dog breathes with its mouth closed, the tongue dissipates a modest amount of heat. But during full panting, heat loss through the tongue increases roughly eightfold, reaching nearly 500 joules per minute at peak respiratory rates. Blood vessels in the tongue dilate during panting, flooding the surface with warm blood that loses heat as saliva evaporates. It’s essentially a radiator that the dog can deploy on demand by opening its mouth and letting the tongue hang out.
How the Tongue Works as a Drinking Tool
Dogs drink in a surprisingly complex way, and tongue length plays a direct role in how much water they capture per lap. High-speed video analysis published in the Proceedings of the National Academy of Sciences revealed the full mechanics: a dog extends its tongue, curls the tip backward into a ladle shape, and slams it into the water surface. This creates a splash. As the tongue retracts, fluid sticks to the top surface and gets pulled upward, forming a column of water that rises out of the bowl.
The dog then snaps its jaws shut at the exact moment the water column is about to break apart, capturing the liquid. The tongue retracts at remarkable speeds, between 0.7 and 1.8 meters per second, with accelerations reaching one to four times the force of gravity. That backward curl isn’t just for show. It increases the effective diameter of the tongue’s contact with the water, pulling up a larger column than a straight tongue would. This is also why dogs are messy drinkers: the bigger splash is a trade-off for getting more water per lap.
X-ray imaging has confirmed that most of the water scooped by the curled underside of the tongue actually falls away. The liquid that makes it to the throat is almost entirely the water clinging to the top of the tongue during retraction. A longer, wider tongue creates a bigger column and delivers more water with each lap cycle.
A Muscular Hydrostat
The tongue belongs to a category of biological structures called muscular hydrostats, which also includes octopus tentacles and elephant trunks. These structures contain muscles arranged in three perpendicular directions, allowing them to change shape without any skeletal support. The tongue doesn’t shorten or lengthen like an arm bending at a joint. Instead, it deforms by squeezing one region to bulge another, preserving its overall volume while shifting its shape dramatically.
In dogs, the main protruding muscle of the tongue has two distinct subdivisions, each controlled by separate nerve branches. This gives dogs fine control over both the extension and curling of the tongue, which matters for everything from lapping water to cleaning hard-to-reach fur to picking food scraps off the floor. The result is an organ that can extend well beyond the mouth, curl in multiple directions, and apply varying pressure, all without a single bone inside it.
Grooming, Bonding, and Communication
Dogs use their tongues socially from the moment they’re born. Mother dogs lick newborn puppies to clean them, stimulate breathing, and prompt urination and defecation during the first weeks of life. Puppies quickly learn that licking is a core social behavior. Young dogs lick older dogs’ faces as a signal of submission and friendliness, clearing the way for safe interactions. Adults lick each other for mutual grooming, affection, and to communicate that they mean no harm.
When dogs lick people, they’re tapping into this same behavioral toolkit. Your hands, face, ears, and feet carry concentrated salts and oils from sweat glands that dogs find appealing. The palms of your hands and your forehead produce a thin, salty fluid, while your ear canals and eyelids secrete thicker substances that mix with skin bacteria to create distinctive smells. Dogs can taste bitter, salty, sweet, and sour, and licking also enhances their sense of smell by bringing scent molecules into closer contact with their olfactory system.
Licking also has a self-soothing function. It triggers the release of endorphins in the dog’s brain, producing a calming effect, followed by a boost of dopamine. A longer tongue makes all of these activities more effective, whether a dog is grooming a hard-to-reach spot on a packmate or thoroughly cleaning a wound on its own body.
Why Some Breeds Have Bigger Tongues
Tongue size varies considerably across breeds, and the differences aren’t always proportional to body size. Flat-faced (brachycephalic) breeds like French Bulldogs, English Bulldogs, and Pugs have tongues that are disproportionately large relative to their shortened skulls. CT scans comparing these breeds found that French Bulldogs and English Bulldogs have significantly greater tongue volume relative to body weight than Pugs, even among dogs of similar size.
This isn’t necessarily a good thing. Macroglossia, a clinical term for an abnormally large tongue, is now recognized as a component of brachycephalic obstructive airway syndrome. In these breeds, the tongue hasn’t shrunk to match the compressed skull, so it crowds the airway. Increased fat deposits within the tongue tissue contribute to the problem, similar to how tongue fat causes obstructive sleep apnea in people. So while a long tongue is an advantage for most dogs, in breeds with drastically shortened faces, the mismatch between tongue size and available space creates breathing difficulties.
At the other end of the spectrum, long-snouted breeds like Greyhounds and Collies have tongues that fit comfortably within their mouths but can still extend impressively when panting or drinking. For these dogs, tongue length is well matched to skull proportions, giving them efficient cooling and drinking without airway compromise.