Food allergy is quite uncommon and normally causes symptoms within a few minutes of eating the offending food or being in contact with the relevant substance. It is caused when the body mistakenly makes an antibody (IgE) which ‘fights off’ the food when it is eaten (or sometimes is just in contact with the skin). The symptoms are usually those of ‘classic’ allergy such as a red raised, itchy rash (urticaria), wheezing, vomiting, severe gut symptoms or (very rarely) sudden collapse. Most people will therefore already recognize that the food causes them a problem. There are reliable blood tests and skin tests, available through the NHS, that can be used quite accurately to confirm the presence or absence of food allergy.