▲Shellfish, milk, peanuts, eggs, and soy are some of the most common and severe food allergies.

▲According to the largest in-depth survey regarding food allergies among adults, more than 10% of American adults have one or more food allergies.

▲A full 19% of the 40,443 surveyed adults believed they had a legitimate food allergy, but actually don't.

▲Only half of the adult food allergies identified by the survey had been diagnosed by a doctor. Half of the people with allergies didn’t know!

▲Half of the adults with allergies didn’t know they had allergies, and yet nearly half of the people who thought they had allergies actually don’t.

▲Food additives or chemicals (artificial sweeteners, caffeine, artificial colors/flavors), medications, and certain ingredients—such as lactose—may create symptoms like cramping, diarrhea, or vomiting.

▲Many people believe that the only difference between a food allergy and a food intolerance is the severity of the reaction. False!

▲Many others believe that people with food allergies can still eat small amounts of the troublesome food without warranting a reaction. Also false!

▲A true food allergy means that consuming any amount of the allergen, even as tiny as a crumb, will immediately trigger the immune response. The severity of the reaction does, however, depend on the severity of the allergy.

▲Signs of a food intolerance include diarrhea, belly pain, and itchy, swollen lips, many of which overlap with mild food allergy symptoms, hence the confusion.

▲A food allergy happens when your immune system overreacts to a specific food protein. Food intolerances, however, do not involve the immune system.

▲Many people believe they’re allergic to certain fruits, nuts, and vegetables because they get an itchy mouth, scratchy throat, or swollen tongue/lips. It looks and feels like an allergy, but it might not be…

▲They share symptoms like bloating, gas, diarrhea, constipation, headaches, and skin rash, but celiac causes damage to the lining of the small intestine, whereas an intolerance does not.

▲People with a food intolerance can sometimes have small amounts of the offending food without triggering symptoms. And, when the symptoms are at their worst, they are usually confined to the gastrointestinal tract.

▲Antihistamines like eye drops, nasal sprays and pills can help stop the pesky sneezing, itchy eyes, and runny nose.

▲It’s important to visit a doctor if you think you’re allergic to something, as some conditions are treatable, while others are life-threatening.

▲Keep a food diary to record what you eat, when you have symptoms, and what they include. If you notice that a food or ingredient consistently gives you discomfort, it’s likely an intolerance.

▲Factors like pollen, mold, dust, along with cats and dogs, can cause allergic symptoms such as rhinitis and asthma. You can also be allergic to insect venom from bites or stings.

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Avoidance! Steer clear of the substances that upset your body.

▲Symptoms can range from mild (rashes, hives, itching, swelling, etc) to severe (trouble breathing/swallowing, anaphylactic shock, vomiting, loss of consciousness, etc). Most importantly, a food allergy can be life-threatening.

▲Less than a quarter of adults with a real food allergy carried an epinephrine pen, which is the only way to stop a fatal reaction.

▲Only 10.8% described accurate severe reactions of a real food allergy.

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The reaction may actually just be triggered by common pollen allergens crossing with the food’s protein. Symptoms should go away quickly. Plus, if you eat the vegetables cooked, you’ll avoid the reaction completely.

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Once you have a good idea which foods might be causing your symptoms, try excluding them from your diet one at a time (for at least two weeks) and observing the effect.

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A milk allergy is an abnormal response by the body's immune system to milk and products containing milk (most commonly cow). Symptoms can include wheezing, vomiting, hives, and digestive problems, as well as life-threatening anaphylaxis.

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People who are lactose intolerant are missing the enzyme lactase, which breaks down lactose found in dairy. Therefore, people with lactose intolerance are unable to properly digest these foods and may experience nausea, cramps, gas, bloating, and diarrhea.

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Celiac disease is an adverse reaction to the protein gluten (found in wheat, rye, and barley), and is more similar to a food allergy as it involves an immune reaction. It doesn’t, however, involve the antibody responsible for anaphylaxis.

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Interestingly, nearly half of the allergies recorded in the study were developed as adults.

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How Stuff Works focused particularly on the American population, which has an increasing number of kids with serious food allergies (one in every 13). It's changed things like school cafeterias and airplanes, for example.

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Allergies and intolerances plague thousands of lives, shifting diet trends, raising questions about our biology, and making it a real pain when you’re cooking for a big group of people. Do you believe you have a food allergy? Are you unsure about gluten and dairy? It turns out nearly half of everyone who thinks they have an allergy really just has a manageable intolerance. Click through to finally clear up the confusion.