Causes of Sudden Aggression in Cats

Learn the reasons why cats might attack suddenly.

Picture this: You're at the kitchen counter cutting up vegetables. Your cat is sitting in the window box, content and happy. You walk over to the refrigerator to get some radishes and suddenly, out of the blue, your cat races over and attacks your ankles. You're hurt and stunned. What happened?

Dealing with aggression in cats is no fun, and when it's sudden aggression from an otherwise mild-mannered cat, it can be downright baffling and frustrating. We've gathered the main reasons cats engage in sudden aggression here to help you figure out what's going on.

Painful Medical Conditions

Cats that are in pain or not feeling well often resort to aggression in an attempt to defend themselves. They don't always understand that the source of their pain or discomfort is internal and will lash out at a pet or person near them when they feel it. They might also do so offensively as a way to keep someone from aggravating a painful condition they are enduring.

Arthritis, dental disease, abdominal pain, and infections are common causes of pain in cats that aren't readily visible. These conditions can "hide" and cause strange behavior in the cat, including aggression.

If your cat suddenly engages in aggression when he has previously been gentle, the first step is always to visit the veterinarian. Once a medical cause for the problem is ruled out, you can continue on to evaluate the following behavioral causes of sudden aggression.

Fear-Inducing Situations

Cats may become aggressive when they are afraid and don't feel like they have a way to get out of the situation. If something startles a cat, like a loud noise or sudden movement, the kitty might attack the closest person or pet in an attempt to defend himself.

Sometimes it's hard for humans to identify fear or stress-inducing situations or things in a cat's life. Take a look at this article to learn some of the common ones: "6 Common Causes of Fear or Stress in Cats."

Territorial Spats

Cats are territorial and sometimes that leads to aggression within a household. This is most common in multi-cat homes, but cats can also become territorial with people or dogs. Some cats are also territorial over their main human so they might attack you when you try to pay attention to another pet in the home.

If your cat blocks you or other pets from entering certain areas by becoming aggressive, territorialism might be the cause. You might be able to relieve some of this type of aggression by adding more cat scratching posts, litter boxes, and food and water stations, so other cats don't need to use the ones the territorial cat claims. Feliway Multicat can also help tremendously to calm this type of aggression.


This type of aggression occurs when a cat is enjoying receiving petting from a person but then suddenly turns and snaps at the person's hand. This can be quite baffling and seem like the cat has multiple personalities.

Some cats are quite particular about what parts of their body they like to be touched on, and if someone encroaches on an area they don't like, they'll bite. Other times, they are enjoying the petting, but can quickly be irritated by it if it becomes repetitive in the same spot.

Redirection of Energy

Redirected or misplaced aggression is common in cats and can be difficult to diagnose and treat. The situation described in the opening paragraph of this article is most likely the result of redirected aggression.

A cat that is super excited, irritated, or stressed by a trigger that is beyond their reach might turn and attack something or someone totally different to release that energy.

The most common cause of redirected aggression is when a cat sees or senses another cat outside in the yard. The indoor cat can't get to the outdoor cat to defend his territory and he gets all worked up about that. So when you or another pet in the home walks by, he attacks.

Signs a Cat Might Attack

Regardless of the cause of aggression, it can help you deal with it if you know the signs that an attack is about to happen. Many times, a cat that is thinking about attacking will display some or all of the following body language:

  • Dilated pupils
  • Staring intently
  • Stalking
  • Arching the back
  • Whipping the tail back and forth in a jerky manner
  • Raising the hair on the back
  • Laying the ears back
  • Hissing

If you see your cat doing those things, try to redirect him. Throw a toy away from yourself. Don't make eye contact, and move away. Ignore the cat until the signs of aggression are gone.

Disclaimer: This website is not intended to replace professional consultation, diagnosis, or treatment by a licensed veterinarian. If you require any veterinary related advice, contact your veterinarian promptly. Information at is exclusively of a general reference nature. Do not disregard veterinary advice or delay treatment as a result of accessing information at this site.