Suddenly your household cats who have always played together started fighting and these fights are getting serious. You don't like the uproar in the house and you are afraid that they will hurt each other. How can you make them stop fighting and be friends again?
One of the girls may have a medical problem. If one of them has a painful sore, she may be trying to make the other cat to leave her alone. If one of them has not been spayed, one or both of them may have entered puberty, and they may be fighting simply because they feel out of sorts. A third possibility is that the aggression is being triggered by something outside the house. If their territory has been invaded by a dog or cat they can see but they can't reach, the girls may be attacking each other in frustration. Removing the cause of the problem will end the battles. Your vet can help you determine if the cause is medical.
What To Say And Do If your vet can find no medical reason for a cat to be at odds with the other cat, look for signs that their territory has been invaded. Check for stains around the bottom of outside doors and windows that indicate another cat has sprayed. Look for dog droppings in the yard and check for paw prints or broken plants in the flower beds near the house. Some people allow their dogs outside without supervision to relieve themselves, and they may not be aware that their dog is using your yard for his toilet and upsetting your cats. Any sudden change in behavior may signal medical problem. Check with your vet so you can catch problems early, while they are still treatable.