Those who are at the highest risk for allergy induced autism are children who have regressive autism - that is, those children who develop normally who then start to regress at around the age of two years old - and children with behavioral and neurological problems in combination with extreme digestive issues (such as intractable constipation).

Such children are generally incapable of metabolizing (digesting) important common food proteins; specifically casein and gluten. Casein is one of milk's main proteins and is also commonly used in the manufacturing of many common food products. Gluten is a protein found in wheat and several grains and is also often added in the manufacturing of food making them hard to avoid.

For some children with autism, gluten and casein are not digested in the normal way. Instead, they are metabolized only partially and become a substance with similar properties to morphine, which can pass through the wall of the digestive tract and enter the blood stream.

These children also often have a "variant" form of protein in their urine after ingesting casein or gluten. This protein is believed to be the byproduct of the creation of the morphine-like substance; the result of which are disconnected or altered behavior in children and a strong addiction to foods that contain casein and gluten in order to replicate the morphine-like side effects.

Due to this improper digestive functioning, these children are also generally incapable of eliminating many of the chemicals they absorb from within their environment and their food. These can include pesticides, pollution, detergent additives, artificial colorings and flavorings, chemical food additives, and other substances that can become toxic when allowed to build up to unusually high quantities.

The symptoms of autism will typically present themselves within a child's first three years. While some autistic children may have intolerance to chemicals in food, other substances can impact other children. The most common "culprits" are believed to be corn, sugar, wheat, and citrus fruits. Allergy based symptoms may be completely unnoticeable, however, it is common for children with allergies or intolerance to certain foods to experience low blood sugar, excessive sweating (particularly at night), bloating, diarrhea, incapability to regulate body temperature, rhinitis, a redness in the face and/or ears, and under-eye circles when eating the items they are allergic or intolerant to.

The reduction or elimination of problem substances from a child's diet will not cure their autism, but it can help to reduce some of the symptoms of allergy induced autism. This dietary elimination approach has been found to be effective in many children and adults. The improvements reported have been significant in some cases, but for many children, who appeared to be severely autistic, restricting their diet has reduced their symptoms only as long as they don't deviate from the strict dietary limitations.