Probably the oldest established allergy to food is hypersensitivity to gluten. It is a sticky protein that is found in wheat, rye, oats and barley and gives rise to the special gluey cooking texture these foods have.
The result of a gluten allergy used to be a very serious wasting condition known as celiac disease or sprue; the patient simply starved with malnutrition, despite eating adequately. It was eventually discovered that gluten allergy was damaging the lining of the intestine so that it couldn’t perform properly. This meant that food was not being digested and absorbed properly.
Another condition known to have a definite connection width gluten sensitivity is dermatitis herpetiformis. This is a blistering, intensely itchy rash that usually affects the outer surface of the elbows, buttocks and knees but can occur on any part of the body.
Personally, I think that a lot of the people who get well on a gluten-free diet do so because they are wheat allergic. They can tolerate rye, oats or barley with impunity, so gluten cannot be the offender.
Try a gluten-free diet if you are suspicious, but you must be prepared to stick at it for a minimum of six to eight weeks to be sure of feeling any benefit.