Like any other personality trait, autism varies with each individual, ranging from high-functioning to low-functioning. Autism is what is called a spectrum diagnosis. Some autistic people cannot function in ordinary life and seem withdrawn from the world. Others live ordinary lives but still have trouble with social situations and communication and can seem eccentric, single-minded, or awkward when confronted with average social interaction.

Very often, it seems like autistic people process the world in a different way they have a slightly different understanding of reality and respond to input in ways that deviate from the norm. Sometimes these reactions can be violent or aggressive in nature, in some cases due to an input overload or under stimulation. It is thought that part of what causes autistic symptoms comes from a problem in the brain that does not integrate many sensory stimuli, like the integration of touch, sight, and taste to experience a piece of fruit.

There is no real stringent criteria for autism, and any of the following symptoms can be present or absent in a person with an autistic diagnosis. The three main criteria for autism, though, must be present. The first is social interaction impairment, problems in communication, and limited interests coupled with generally repetitive behavior. The following symptoms can be present in a person with autism, but symptoms vary from person to person and depend on the severity of the disorder.

Autistic people sometimes exhibit a resistance or reluctance to embrace change and prefer things to stay the same - some people with autism can become agitated or even angry when their routine is changed in some way. They can have difficulty communicating a want or need and resort to hand motions. They sometimes exhibit excessive over activity or underactivity as well as difficulty with large or fine movements. Repetition of language or movements is a common autistic trait (and in the case of movements can be self-destructive like head- or wrist-banging), as well as obsessive attachment to objects. Similarly, some autistic people have a single interest in their life like math, cats, hearts, or toy cars. Autistic people sometimes exhibit out-of-place emotion like laughing or crying without any discernible reason. They can also have an over sensitivity or under sensitivity to pain as well as trouble recognizing dangerous situations.

Regarding social skills, autistic people can be loners or introverts and do not want to be in social situations - this sometimes comes from an inability to initiate or maintain social interaction. Affection, physical expressions of affection, or common physical interactions may be ignored or denied. They sometimes have trouble maintaining eye contact, communicating in a concise and/or linear fashion, or recognizing social cues, and they may have trouble imitating other people's social interaction themselves. At times, an autistic person might be uncommunicative and unresponsive to any sort of verbal interaction and act as though deaf even though tests indicate that hearing is fine. Some people with autism do not speak at all or exhibit language delay. They can have trouble using their imagination in play or understanding metaphors, jokes, and sarcasm.