Your allergist may recommend allergy tests. This may include skin testing. In an allergy skin test, a very small drop of a liquid food extract, one for each food, is placed on the skin. The skin is then lightly pricked. This is safe and generally not painful. Within 15 to 20 minutes, a raised bump with redness around it, similar to a mosquito bite, may appear. It shows that you are probably allergic to that food and you probably need food allergy treatment.
Sometimes, an allergy blood test may be used. The blood test generally costs more than skin testing. The results are usually not ready for one to two weeks.
If done right, skin tests or blood tests are reliable and can rule in or out food allergy. Some people do test "allergic" to a food (by skin or blood testing) and yet have no symptoms when they eat that food. To confirm test results, your allergist may ask you to do a challenge test. This means that you have to eat or drink small portions of a food in increasing amounts over a period of time to see if an allergic reaction occurs. This is usually done under a physician’s supervision.
How do allergists tell which foods make me sick?
Some people know exactly what food causes their allergy. They eat peanuts or a product with peanut in it and immediately break out in a rash. Others need a doctor’s help in finding the cause. Sometimes, the symptoms show up many hours after they have eaten the food.
Your allergy treatment will typically begin with a complete medical history. Your allergist will ask you about:
- The symptoms you have after eating the food
- How long after eating the food these symptoms occur
- How much of the food you had
- How often has the reaction occurred
- What type of medical treatment, if any, you had
- The medical history will also include questions about your diet, your family's medical history, and your home and living area.
Your allergist asks these questions to find out what is causing your allergy or making your symptoms worse. Allergy to pollen in the air, such as ragweed pollen, can be the cause of the swelling or itching in your mouth and throat if you eat certain foods like melons. There is no food allergy cure.
Can special diets help pinpoint the problem?
Your allergist may narrow the search for foods causing allergies by placing you on a special diet. You may be asked to keep a daily food diary. It lists all food you eat and medication you take, along with your symptoms for the day.
If only one or two foods seem to cause allergies, you may try avoiding them. In this diet, you do not eat the suspect food at all for one to two weeks. If the allergic symptoms decrease during that period and flare up when you eat the food again, it is very likely the food causing your allergy.
However, which food you should avoid (and for how long) and when you should eat the food again (if ever) should be decided together with your allergist. You should never try to eat even a small quantity of any food you and your allergist have decided against.
Your allergist may want to confirm these diet tests with a challenge test. Food allergy testing is a very important step.