Why might a cat become aggressive or bite when it is ill or injured?

When a cat is ill or injured, it may become aggressive or bite primarily because it is in pain. In such states, a cat’s natural instinct is to protect itself, and it may perceive handling or interaction as a threat to its vulnerable condition.12

Because cats have a survival instinct to hide signs of illness to avoid appearing vulnerable to predators, behavioral changes like aggression are significant indicators that a cat requires veterinary attention. It is important to avoid handling a cat that is displaying signs of fear or anger, as cat bites can be particularly dangerous due to the bacteria present in their mouths. If you notice sudden aggression, a professional checkup is essential to determine if an underlying medical issue is the cause.12