There are different types of non-immune reactions to food, known as food intolerances. These are generally not "dangerous" to the patient, but can cause irritability or discomfort. Intolerances are more common in adults than children, so in children, an allergy always needs to be excluded first.
Most people with food intolerance will tolerate small amounts of a certain food, only to become symptomatic if they have too much of it, for example wheat in people with irritable bowel syndrome . It can also build up over a period of days, after consuming various foods containing the same problem substance. Symptoms can occur immediately, or be delayed by up to 24 - 48 hours, which can often make it difficult to determine what is causing the food intolerance.
Some people who lack the enzymes necessary to digest certain foods. A common example is lactose intolerance. This is due to the lack of the enzyme "lactase," which is essential for the digestion of the milk sugar lactose. Such a deficiency may be inherited or occur temporarily after a bad bout of gastroenteritis. A deficiency of the lactase enzyme leads to cramping and diarrhoea after the intake of dairy products.
A further example of non-allergic food intolerance is the reaction caused by naturally occurring chemicals in food, or by food additives (chemical reaction). These reactions are similar to true allergic responses and may be mistakenly labelled as food allergy. Food additives include a variety of substances, such as preservatives, flavouring agents, colouring agents, salicylates (aspirin like substances) etc. Well-known examples are tartrazine, monosodium glutamate (MSG), sulphur dioxide and benzoates.
Other foods which can cause an intolerance include: