Many factors can cause stress and what one cat may find stressful, another may not. However, cats are often stressed by a change in their lifestyle, routine and/or environment. Examples include a visit to the vets, a stay in a boarding cattery, a new baby, other cats in the neighbourhood, building works or renovations to the home, or a new pet. For sensitive cats, something as minor as a new piece of furniture or a change in position of the litter tray can be stressful. Cats are naturally solitary animals and living in a busy household being forced into close proximity with other pets can be a stressful experience for some cats. Individual cats handle stress in different ways some become quiet and reserved, others spray in the house and some may simply move out!
The other common behavioural problem exhibited by cats is aggression. The two main reasons for aggression to develop in cats are because of fear, or because they have learnt an inappropriate way of interacting with their owner. Fear aggression is a defence strategy, which occurs when the cat is feeling threatened. Play behaviour can be termed aggressive when it is directed at an inappropriate target, eg human hands and feet.
All behavioural problems are most easily dealt with before they have become well established. If your cat shows any unusual behaviour or any undesirable habits then contact your vet in the first instance for advice.