Food intolerance is an adverse reaction to a food triggered by a food or food component, e.g. lactose intolerance. It does not involve the immune system. The reaction is due to non-digestion/absorption of a specific food or food component.

For example, people with lactose intolerance do not have the enzyme lactase to digest the sugar, lactose, in milk. This is one of the most common food intolerances occuring in nearly 50% of the adult world population.

Some people have an intolerance against additives such as flavour enhancers (MSG) or preservatives (sulphite). The symptoms vary widely between individuals and it is often impossible to determine which food component causes which reaction.

The symptoms of food intolerance can be mistaken for those of a food allergy. It is important to consult a physician to determine the causes of a reaction to food.