If you develop a headache, itching, or hives shortly after eating, you might have a food allergy. Food allergies are often difficult to pinpoint since there are so many additives in prepared foods and several foods and spices in a single recipe. You'll probably need to undergo allergy testing to find out what foods you need to avoid. These are some of the tests your doctor may use to identify the foods that trigger your allergies.
A scratch test is a simple allergy test that's done in your doctor's office. The test is done on your arm or back. Your skin is scratched in several places with needles that contain various food allergens. The test isn't painful, but if you have an allergic reaction to a substance, it may cause your arm to develop hives or itch in the area. This test can reveal what foods you're allergic to, but it usually tests for the most common allergens. It isn't comprehensive or completely reliable, so your doctor may order other tests along with the scratch test.
If your doctor orders a blood test, you'll have a sample of blood drawn and sent to a lab. At the lab, your blood will be exposed to a range of allergens to determine the ones that trigger a reaction. This test, when combined with a scratch test, will give your doctor a good idea of your trigger foods. However, your doctor may also want you to try an elimination diet.
To do this, you begin with a very restrictive diet that includes foods that rarely trigger allergy symptoms. Other foods are gradually added back into your diet until you have an allergic reaction. This is a long process, but it helps you develop a list of safe foods you can eat while you're working on identifying the ones that trigger your allergies. When you eat a food that causes hives, itching, headache, or other symptoms, you can eliminate it from your diet and avoid the symptoms in the future. While you're on this diet, your doctor may have you keep a food diary that tracks everything you eat as well as any symptoms you have that day. A diary is valuable at helping you notice patterns you might miss otherwise.
Once you and your doctor have identified the foods that give you trouble, you'll know what you need to avoid to keep your symptoms under control. However, avoiding food allergens is often difficult, especially when you dine at a restaurant, or when you eat food someone else has prepared. You can never be certain what is in your food unless you make it from scratch yourself. For that reason, you should be prepared to deal with an allergic reaction if it occurs. Your doctor may prescribe antihistamines for your allergy flares, or even an epinephrine injector if there is a risk of a severe reaction.