Why does my cat bite or nip me, even out of nowhere?

Cats hide pain very well, so a bite may be the only sign. A cat that hurts may bite when a sore spot is touched, when it is lifted, or when it expects to be handled. Common causes are stiff joints (arthritis), sore teeth or gums, itchy or inflamed skin, an abscess, or a bladder or gut problem. If the biting is new and fits one touch or movement, think of pain first and see a vet.

Some illnesses make a cat irritable or less happy to be touched: an overactive thyroid (mostly in older cats), nerve problems, sight loss, high blood pressure or kidney disease, and confusion in old age. A rare condition makes the skin on the back roll, with frantic licking and biting. Rabies can also cause sudden aggression. Only a vet can tell these apart.

The most common reason a friendly cat bites the hand that was just stroking it. Many cats like touch only in small amounts, and stroking the same spot adds up until the cat has had enough. The bite means stop. Many cats then jump off the lap and walk away. Belly, base of the tail, back, paws and legs run out fastest; head and cheeks are usually safe.

Kittens and young cats practise hunting on anything that moves. A cat that was allowed to wrestle with fingers learns that hands are toys, and the bites hurt more as it grows. It is more likely in cats taken from their mother early, raised without littermates, left alone a lot or short of play.

A soft, careful nibble during a cuddle is not aggression. Cats groom each other with their teeth and lips, and some nibble their people the same way, often while purring. Experts read a soft nip followed by licking as grooming and a sign of affection. No study has tested it, but it is the common expert reading. See also why your cat licks you.

A cat with no outlet for hunting may stalk you instead. It hides round a corner or under furniture, crouches, wiggles its hindquarters and pounces on your feet or ankles as you walk past. It happens mostly in indoor cats, single cats and young cats, often at dusk and dawn. It is play with a moving target, not anger.

A scared cat first tries to get away or hide. It bites or swipes only when it cannot escape, or when someone reaches for, grooms or lifts it. Little contact with people as a kitten, rough handling and past punishment make fear biting more likely. Loud noises, strangers and vet visits can set it off.

A cat worked up by something it cannot reach, such as another cat outside the window, a loud noise or a stranger, may bite the person or pet nearby. It then looks like a bite from nowhere. The cat can stay worked up for half an hour, hours or even days, so the bite can come later.

A new pet, a move, a changed routine, noise or too little space raise stress, and a stressed cat has less patience. A bored indoor cat looks for action. A cat that wanted play or food and got petted instead can also bite out of frustration. Stress biting is more general and harder to predict than pain biting.

If a bite makes the touch stop, or brings attention, play or a treat, the cat learns that biting works. Biting for attention often happens in the evening or when you are in bed, because cats are most active at dusk and dawn. A shriek or a quick game rewards it without meaning to.