To determine the cause of aggressive behavior, consider how and when it started, the circumstances under which it occurred and what the various attacks may have in common. True aggression should be distinguished from play-fighting. In most cases, feline aggression results from the lack of trust, fear, or stress. During socialization, a kitten learns to relate to and trust humans. This trust must be strong enough to overcome the natural fear and avoidance behavior seen in cats that grow up in the wild. Cats that miss the period of primary socialization at three to nine weeks of age may never make a good adjustment and will always retain some anxiety when confronted by strange people.
Many cases of unexplained aggression are brought on by environmental stress leading to heightened fear. A distressed cat may suddenly attack someone nearby, even though that person played no part in causing the upset. A cat that has just been in a fight may accept handling by one person, yet scratch and bite another who approaches too closely. When cornered, a frightened cat will nearly always take aggressive action. Some cats, when they are rubbed vigorously under the belly or along the back near the tail, will turn suddenly and scratch or bite. These cats are saying "no" to petting. Some cats like to be petted, others do not. In some cases, aggressive behavior develops as a result of an underlying disease or discomfort. For example, cats with a thyroid gland disease often become aggressive; hunger and physical stress may also induce irritable behavior.
A poorly socialized cat should be allowed to retreat from threatening situation and not forced to confront the causes of anxiety. These cats are often "one person" cats. They make excellent companions but must be watched carefully around strangers, particularly children. A frightened cat that resists handling should be left alone until relaxed. Minimize all stimuli that impose stress and cause fear. One way is to feed the cat. Sit alongside as the cat eats and speak soothingly. Soon, the cat will come to you for petting. Cats that like to be petted or handled on their own terms should be respected as individuals and treated accordingly.