Some dog "facts" get repeated so often they're treated as common knowledge — even though they were debunked by science years ago. Here are 12 of the most persistent dog myths, and what's actually true.
Myth 1: "One Dog Year Equals Seven Human Years"
The truth: This math has never held up. Dogs mature much faster than humans early on — a 1-year-old dog is already roughly equivalent to a 15-year-old human in physical and sexual maturity — then the aging rate slows down and varies enormously by size. A 2020 study in the journal Cell Systems proposed a formula based on DNA methylation showing small breeds age more slowly in their later years than large breeds, which age faster and have shorter overall lifespans. There is no single, accurate multiplier that works for every dog.
Myth 2: A Wagging Tail Always Means a Happy Dog
The truth: A wagging tail simply means a dog is emotionally aroused — which could be happiness, but could just as easily be anxiety, frustration, or the lead-up to aggression. Research on tail-wag asymmetry has found that dogs wag more to the right when they feel positive and more to the left when they feel negative, and other dogs can actually perceive this asymmetry. Speed and height matter too: a slow wag with a low, stiff tail is a very different signal than a loose, full-body wag.
Myth 3: Dogs See Only in Black and White
The truth: Dogs are dichromatic, meaning they have two types of color-detecting cones instead of the three humans have. They see blues and yellows clearly but have trouble distinguishing reds and greens — similar to red-green color blindness in humans, not a grayscale world. This is why orange toys can be genuinely hard for a dog to spot in green grass.
Myth 4: A Warm, Dry Nose Means a Dog Is Sick
The truth: Nose temperature and moisture fluctuate constantly based on sleep, hydration, weather, and simply how recently a dog licked its nose. A warm or dry nose on its own is not a reliable sign of illness. Real signs of sickness — lethargy, vomiting, appetite loss, behavior changes — are far more trustworthy than nose temperature.
Myth 5: Dogs Eat Grass Because They're Sick
The truth: Studies observing dog behavior found that fewer than 10% of grass-eating episodes were preceded by signs of illness, and vomiting occurred afterward in less than 25% of cases. Most veterinary behaviorists now believe grass-eating is largely normal exploratory or dietary behavior in healthy dogs, not a signal of an upset stomach.
Myth 6: A Dog's Mouth Is Cleaner Than a Human's
The truth: Dog mouths are not "cleaner" — they simply host a different set of bacteria than human mouths. Some bacteria found in dog saliva (like certain strains of Pasteurella) can cause infections in humans if a bite breaks the skin. Dog and human mouths aren't directly comparable in "cleanliness" because the bacterial makeup is so different.
Myth 7: You Can't Teach an Old Dog New Tricks
The truth: Dogs of any age can learn new behaviors — older dogs may simply learn at a different pace or have established habits to work around. Cognitive training is even recommended by veterinarians for senior dogs, as mental stimulation has been shown to help slow age-related cognitive decline, similar to its effects in humans.
Myth 8: Dogs Feel Guilty When They've Misbehaved
The truth: A well-known 2009 study by canine cognition researcher Alexandra Horowitz found that the "guilty look" dogs make appeared just as often whether or not the dog had actually misbehaved — and appeared most strongly when the owner scolded them, even if the dog was innocent. The expression is more likely a response to a human's tone and body language than an internal sense of guilt.
Myth 9: Pit Bulls Have "Locking Jaws"
The truth: No dog breed has a jaw mechanism that physically locks. Multiple veterinary anatomical studies, including ones conducted at the University of Georgia, found no structural difference between a Pit Bull-type jaw and any other dog's jaw. The myth likely persists because of how tenaciously some individual dogs grip during play or a bite, which is a behavioral trait, not an anatomical one.
Myth 10: All Dogs Are Natural Swimmers ("Doggy Paddle")
The truth: While many dogs instinctively paddle when placed in water, plenty of breeds are poor swimmers or can't swim at all — particularly brachycephalic (flat-faced) breeds like Bulldogs and Pugs, and very short-legged, heavy-chested breeds like Basset Hounds and Dachshunds. Never assume a dog can swim safely without supervision, regardless of breed.
Myth 11: Rescue Dogs Are More Likely to Have Behavior Problems
The truth: Studies comparing shelter-adopted dogs to dogs acquired from breeders have found no consistent evidence that adopted dogs have more behavior issues overall. Behavior is shaped far more by individual history, training, and socialization than by whether a dog came from a shelter or a breeder.
Myth 12: A Dog Only Barks to Get Attention
The truth: Barking is a multi-purpose communication tool, not a single behavior with one cause. Dogs bark to alert, to express excitement, out of fear or anxiety, out of boredom, in response to other dogs, or to communicate a need like wanting to go outside. Effectively addressing excessive barking requires first identifying which type it is — see our excessive barking guide for the full breakdown.