Delayed food allergies can appear more than 48 hours after eating the offending foods. If the foods are eaten every day, they will cause chronic symptoms.
This differs from immediate hypersensitivity, also known as anaphylactic allergy. An example of immediate hypersensitivity is the allergy that some people have to peanuts.
That is a specific type of immune reaction that is usually immediate (within half an hour) and sometimes life-threatening. Reactions include hives, angioedema (swelling), and anaphylactic shock. This kind of food allergy is relatively uncommon, but very obvious to the sufferer.
In contrast, many people are unaware of delayed allergies that cause them chronic problems.
A delayed food allergy (also called a food intolerance or sensitivity) can involve almost any symptom. Typical examples of symptoms are headaches, stomach aches, joint and muscle pain, fatigue, sluggishness, or hyperactivity.
Yet we don't realize that the true cause of the symptom is a food!
How is it possible not to know that you have a delayed food sensitivity?
These allergies are, of course, delayed. There is a length of time, up to several days, before you feel an adverse effect. It is difficult to connect it with the food.
Often, it is a food that is eaten every day or frequently throughout the day. The cause of the symptoms is never clear. In addition, allergies to more than one food can mean overlapping symptoms.
There is often a cycle in which the food relieves its own symptoms. You crave and depend on the food to make you feel better. (Technically, the food is relieving an addictive withdrawal.)
For these reasons, it is often impossible to accurately discover delayed food sensitivities without special manipulation of the diet in an elimination diet.