Some people are not aware that they have food allergy. It can be difficult to diagnose especially if allergic reactions are not apparent before. Symptoms of food allergy only appear if you exceed the tolerable amount of foods you are allergic to.
There have been a lot of studies about food allergy that involves patients having asthma. You can easily see the symptoms after a couple of hours after eating a certain kind of food. Asthma and eczema are associated with atopic patients with allergies in food.