There is a phenomenon in the cat world that seems to be foreign to humans: nonrecognition aggression. This occurs when a cat leaves the home – usually, but not always, for a veterinary appointment – and is the recipient of aggressive behavior from the cat who remained at home after returning. This can happen to cats of any age or breed and regardless of the relationship they have; even cats who adore each other have been parties to nonrecognition aggression.
The aggressive behaviors displayed by the stayed-at-home cat can be as minor as hissing at and avoiding the returning cat and as intense as yowling and attacking with teeth and claws. Things may return to normal after a few hours, after days or weeks, or, sadly, never.
Several theories exist as to why the stay-at-home cat responds negatively to the returning cat. These include the returning cat behaving oddly due to recovering from anesthesia or the stress of being at the vet; the aggressing cat being reminded by the medicinal scent on the returning cat of negative experiences; the returning cat looking different following shaving or trimming at the groomer’s or some medical procedures at the vet’s; and, the most likely, the left-behind cat perceiving the returning cat as a stranger because he smells differently (hence the term nonrecognition aggression). Cats identify others by scent far more than by sight. A cat who returns from the vet smelling of rubbing alcohol, treatment products, vaccines, cleaning products, and stress hormones is unrecognizable to the other cat in the home and perceived as an intruder.
The good news is that nonrecognition aggression is highly preventable. The following steps can go a long way to maintaining peace in the home.
- Bring a towel or blanket holding the stay-at-home cat’s scent or both cats’ scents with you when taking a cat to the vet but leave it in the car so it doesn’t pick up odors from the vet office. Place it in the carrier on the way home to allow the familiar scent to transfer to the returning cat.
- Place the returning cat in a separate room once you are home. Feed some treats to each cat on either side of the closed door. Open the door after a couple of hours if the cats are calm or, if the cat who visited the vet is ill, once that cat is healthy (unless the cats seem to be interested in positive interactions sooner).
- Spray Feliway, a synthetic pheromone, before leaving with the cat and after returning. Spray it both in the returning cat’s room and in the areas where the stay-at-home cat spends the most time.
- If the cat who left the house will tolerate it, bathe him or use baby wipes or dry shampoo for pets after returning home to remove the scents of the veterinary office from his fur and skin.
- Take both cats. This does not guarantee that there won’t be problems but, in some cases, when both cats share the same foreign smells there is no negative reaction.
- Choose veterinarians and groomers who have Fear Free or Low-Stress Handling certification! A cat whose normal smell is not affected by high levels of stress hormones is more likely to be recognized by the other cat.
If nonrecognition aggression does occur, the cats will need to be reintroduced as if they are truly strangers. See our articles Introducing a New Cat to Your Other Cats and Improving Cat Relationships with Clicker Training.