Food allergy is an adverse reaction to a food that is mediated or brought about by the immune system. By contrast, food intolerance is a non immune-mediated adverse reaction. Both reactions can cause discomfort and unpleasant symptoms, and both allergy and intolerance can be labelled as ‘food hypersensitivity’. These reactions are different from toxic food reactions (such as poison in non-edible mushrooms, or salmonella infection), which will generally cause a reaction in all humans, not just sensitive individuals.
Adverse reactions to food are common in infants. Cow’s milk protein allergy is one of the most common causes and occurs in 2-6% of infants. Cow’s milk protein allergy is an immune reaction to one or more of the proteins in cow’s milk. It is often confused with lactose intolerance, which is caused by a (usually temporary) enzyme deficiency, not an immune response.