It has been suggested that certain viral infections may cause autism and there is an increased risk in having an autistic child after exposure to rubella during the first trimester of the pregnancy. Although there is no reliable scientific evidence at this time, there is some suspicion that toxins and pollution in the environment may cause autism. The recognition of autism is often possible shortly after birth, but in some cases it may be delayed for months and up to two or three years, until parents identify unusual delays in the development of the child's language, play or social interaction. During childhood, autistic children may show no or limited speech, deficiencies in communication, a preference for being left alone, poor social interaction and play, and defective cognition. Other related problems include unusual responses to people, abnormal attachments to certain objects, difficulties in sleeping and eating, avoiding eye contact, insensitivity to pain, hyper-activity or excessive passivity, and attention deficits.
Many autistic individuals are over-sensitive to touch or to sounds in their environment.
Another characteristic which is quite common in autism is a fear of new experiences and a stubborn insistence on rigid routines, with the slightest change, greatly upsetting the child and often provoking tantrums. Many autistic children do not realize that others may have different thoughts and perspectives than their own. For example, a child may be asked to show a photograph of an animal to another child. Rather than turning the picture around to face the other child, the autistic child may, instead, show the back of the photograph. In this example, the autistic child can view the picture but does not realize that the other child has a different perspective or point of view.