There is a big difference between being allergic to a food and having an intolerance or sensitivity to it.
A true allergic reaction can affect multiple parts of the body and can be life threatening. A food intolerance tends to affect only the digestive system. Getting nauseous or cramps after eating a food could be an allergy or a sensitivity. But an allergy can also produce hives, itchy eyes, tightness in the chest or shortness of breath and, in the most severe cases, anaphylaxis.
“Because of the life-threatening nature of anaphylaxis, it is important to see an allergy specialist if you are unsure if you have a food allergy or an intolerance,” 
said Kanao Otsu, MD, allergist and immunologist at National Jewish Health. “A specialist will take into account your history with that food and test results to properly diagnose the condition.”
While 20 percent of adults report having a food allergy, as many as half might have an intolerance instead, National Jewish Health says.
Kids with Food Allergies, a Doylestown, PA-based organization that's part of the Asthma and Allergy Foundation of America, says food intolerance symptoms come and go and may only happen when a child eats a lot of the particular food.
Reaction to a food allergy, on the other hand, can be triggered by eating just a microscopic amount or even touching or inhaling it, says the American Academy of Allergy Asthma and Immunology.
An allergist can determine whether it is an allergy or intolerance. If it is an allergy, check out these organizations, which advocate and educate about allergies.
If you are inviting someone into your home who has an allergy, here is a guide to preparing a meal that will put everyone's mind at ease, along with several recipes. And here's how to protect your child when you are eating out.
