Sudden cat aggression: Why do cats bite?

Have you ever been peacefully petting a purring cat, only to have them turn around and swat their claws at you or try to bite your hand? Sudden cat aggression, considered hostile or violent behavior intended to dominate or intimidate, is a fairly common behavioral problem in cats. In fact, aggression is the second most common feline behavior problem seen by animal behaviorists, behind issues with the litter box.

Why do cats suddenly exhibit aggression? What can you do to address your cat’s aggressive behavior?

Consequences of cat aggression

Cats are born with five potential weapons: their mouth full of sharp teeth and four clawed paws. Aggression in cats can range from hissing to a full-on attack, which can result in painful injuries to you or other pets and even lead to rehoming your cat. According to the Cornell Feline Health Center, a recent study reported that 27 percent of cats relinquished to shelters for behavioral reasons were surrendered for aggression.

Cats can bite and inflict severe injuries, which are painful and can easily become infected. They can also cause cat scratch fever, a usually benign but potentially serious infectious disease that causes flu-like symptoms. Fights between cats rarely result in fatalities, but they can lead to infections and result in considerable veterinary expenses for cat parents. Aggressive cats can be risky to have at home and can pose a real danger to family and visitors.

Signs of aggression in cats

Feline aggression can occur unexpectedly for a multitude of reasons. It can be difficult to identify signs that a cat may be about to exhibit aggressive behavior. However, aggression in cats rarely comes about entirely suddenly, as there are some subtle warning signs cat parents can keep an eye out for.

Watch out for changes in a cat’s body language, including:

  • Dilated pupils
  • Fast tail twitching or thrashing
  • Direct stare
  • Crouched or arched posture
  • Ears flattened or oriented backward
  • Raised hair along spine
  • Stiff posture
  • Vocalization such as hissing, growling, or yowling
  • Swatting
  • Biting

Reasons for sudden cat aggression

Several different factors can trigger or cause aggression in cats. Being able to identify the reasoning behind your cat’s behavior can help you address any issue or prevent aggression in the future. Some possible reasons for aggression in cats can include:

Fear and stress

If your cat feels threatened, unsafe, overstimulated, or stressed, they may become aggressive as a means of protecting themselves. Changes in the household or environment such as new people, loud noises, other pets, or even different smells can create stress for a cat. While cats can be fearful of new things, they may also exhibit fear or stress if they have developed a negative association based on a previous experience.


Cats that are experiencing discomfort may act aggressively toward people or other pets in an attempt to avoid touch, movement, or certain activities that might worsen the discomfort. Cats are naturally stoic animals and do not show discomfort and vulnerability outwardly, so more subtle behaviors like hiding, decreased appetite, lethargy, or aggression can indicate your cat is uncomfortable. This discomfort may be caused by injury, illness like dental disease, or joint discomfort.


Learning appropriate play is an important part of a cat’s socialization, and this normally occurs during time spent with littermates. Cats learn that they are biting or scratching too hard when their littermates stop playing or retaliate. Cats raised alone during their early lives may not learn this important lesson, so their play style can be interpreted as aggressive.

Territorial behavior

Cats are creatures of habit and routine. Some cats may become protective of their territory if changes occur in their environment or if they feel threatened in their “safe space.” This can happen with visitors or new people or animals in the house or neighborhood. This aggression commonly takes the form of swatting, chasing, and attacking the intruder.



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