Cat Mouths. The Dirtiest of Them All


It’s a common belief that cats’ mouths are cleaner than dogs’ mouths. However, recent studies have shown that this isn’t necessarily true. In one study, researchers actually found more bacteria in cats’ mouths than in dogs’ mouths. This surprising result sparked interest in understanding why cats’ mouths may be dirtier, despite stereotypes suggesting otherwise.

Cats Have More Bacteria

Studies have shown that cats have a wider range of bacteria in their mouths than dogs. One study comparing oral bacteria in humans, dogs, and cats found that cats had the highest number of bacteria species, followed by dogs and then humans ( Part of the reason is likely cats’ more varied diets and hunting behaviors, which expose them to a greater diversity of microbes compared to dogs. Cats are obligate carnivores and often hunt and eat small rodents, birds, and insects, while dogs are generally fed a consistent commercial diet by their owners. The higher bacterial diversity in cats’ mouths is one reason they can transmit more potential zoonotic diseases to humans than dogs can.

Sharp Teeth

Cats have extremely sharp teeth that can cause deep puncture wounds. Their long, pointed canine teeth are designed for seizing prey and can easily penetrate skin when they bite or scratch. According to the VCA Animal Hospitals, a cat’s sharp teeth often leave small but deep puncture wounds that drive bacteria deep into the skin and tissue. These types of injuries are prone to infection since the bacteria is sealed inside the wound.

Cat bites to humans can be especially problematic. As noted by the VCA, most cat bites are small punctures that push pathogenic bacteria far under the skin surface. Without proper treatment, serious infections can develop within 24-48 hours. The sharp teeth allow cats to deliver extremely deep tissue damage from even a small nip.

Saliva Composition

Cats’ saliva contains bacteria that are more harmful to humans. A cat’s mouth hosts over 600 different types of bacteria, many of which can cause illness in humans (source). One study found that a single bite from a cat can infect a human with up to 50 different germs (source).

One of the most concerning bacteria found in cat saliva is Bartonella henselae, the agent responsible for cat scratch disease. This bacteria can infect humans through a bite or scratch and cause swollen lymph nodes, fever, and fatigue (CDC). Another problematic bacteria is Pasteurella multocida which can cause painful wound infections in humans.

While a dog’s mouth also contains harmful bacteria, studies show cat saliva harbors more strains that are infectious to people. Cats do not groom themselves as thoroughly as dogs, allowing more bacteria to accumulate in their mouths over time.


Cats are obligate carnivores, meaning they must eat meat to acquire certain nutrients for survival (Source). Their teeth and digestive systems are adapted for eating meat, not plant material. Dogs, on the other hand, are omnivores and can digest both meat and plant matter. Omnivores like dogs have more varied gut flora containing enzymes capable of breaking down cellulose and other plant fibers (Source). The bacteria in carnivore digestive systems are specialized to process proteins and fats, while omnivore gut flora is more diverse. Cats’ obligate carnivore status means their oral bacteria is highly adapted to metabolize meat, producing more potential compounds implicated in malodor and disease.


Cats are notorious for being clean, meticulous groomers. In fact, cats spend 30-50% of their waking hours grooming themselves by licking their fur and paws (Catster, 2023). This frequent grooming behavior helps distribute natural oils over their coat and allows cats to remove dead hair and skin. However, it also means that cats end up spreading their oral bacteria all over their bodies more than dogs do.

While grooming helps keep a cat’s coat clean and tidy, they are actually spreading bacteria from their mouth to the rest of their body. A cat’s rough tongue picks up a lot of bacteria during grooming sessions. By licking their fur, paws, and other body parts, cats spread these oral bacteria over their skin and coats. One study found that over 20 species of bacteria could be cultured from the fur of healthy cats (PetMD, 2019). So even though excessive grooming looks clean, it actually spreads bacteria.

In comparison, dogs usually only lick specific areas and do not groom themselves all over for many hours a day. This means dogs do not spread bacteria from their mouths over their bodies to the same degree as cats.


Cat bites are more prone to infection than dog bites. Studies have found that 28-80% of cat bites become infected, compared to only 5-25% of dog bites (Rothe 2015). This is likely due to a few key differences between cat and dog bites.

First, cats have very sharp, needle-like teeth that are able to penetrate deeply into skin and tissue (Davies 2000). Their bites often form narrow, deep puncture wounds that seal over quickly, trapping bacteria inside. Dogs have blunter teeth that tend to cause wider crush injuries or tears, which don’t seal as easily and allow better drainage.

Second, cats have more virulent bacteria in their mouths than dogs. Their saliva contains species like Pasteurella multocida and Bartonella henselae, which can cause serious infections in bite wounds (Davies 2000). Dogs’ mouths contain fewer dangerous bacteria overall.

For these reasons, cat bites have a much higher risk of complications like abscesses, septic arthritis, osteomyelitis, and septicemia if left untreated. Prompt medical care, including antibiotic treatment, is essential for cat bite injuries.


Cats can transmit diseases through bites and scratches that are not typically found in dogs. One of the most notable is cat scratch disease, which is caused by a type of bacteria called Bartonella henselae. This bacteria is found in cat saliva and can be transmitted to humans via a bite or scratch, causing swollen lymph nodes and fever (

Another concern is pasteurellosis, an infection caused by the bacteria Pasteurella multocida. This bacteria is found in over 50% of healthy cats’ mouths and can cause painful wound infections in humans after a cat bite ( Pasteurella can even lead to serious complications like sepsis or meningitis if left untreated.

While dogs can also transmit diseases through bites, the types of bacteria found in cat mouths make their bites more prone to cause infections in humans. Proper wound care and antibiotics are important after a cat bite to prevent transmission of feline diseases.


There are several things cat owners can do to help clean their cat’s mouth and prevent the spread of bacteria:

Brushing your cat’s teeth regularly can remove plaque and tartar buildup. Use a soft-bristled toothbrush and cat-safe toothpaste. Take it slow and make it a positive experience for your cat.

Dental treats or kibble can help scrape away tartar as your cat chews. Look for treats approved by the Veterinary Oral Health Council.

Schedule regular veterinary dental cleanings to thoroughly clean your cat’s teeth under anesthesia. Cleanings are recommended at least yearly.

Avoid sharing food or utensils with your cat to prevent transfer of bacteria between you.

Wash your hands after handling your cat, its food, toys, or litter to remove germs.

Disinfect your cat’s food and water bowls regularly to kill bacteria. Stainless steel bowls are easier to sanitize.

Discourage chewing behaviors that can lead to fractured teeth and abscesses. Provide appropriate toys and scratching posts.

Feeding wet food in addition to dry kibble can help clean the teeth. Canned food has higher moisture content.

Regular veterinary checkups allow early detection and treatment of dental disease in cats before it becomes severe.


Both cats and dogs can harbor bacteria and diseases in their mouths that can be transmitted through bites and other contact with their saliva. However, there are a few key reasons why cats tend to have more bacteria than dogs:

  • Cats have sharper teeth that can pierce skin and deliver bacteria deep into wounds.
  • Cats groom themselves constantly, so any bacteria on their skin gets transferred into their mouths.
  • Cats are more likely to be carriers of certain diseases like cat scratch fever.
  • Cats are more likely to bite and have more puncture wounds, providing pathways for bacteria to enter the body.

While cat bites should always be taken seriously, proper care and hygiene can reduce the risks. See your doctor right away if bitten and be diligent about washing hands after contact with cat saliva. With some basic precautions, cat owners can continue to safely enjoy their feline friends.

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