Imagine what life would be like if you had to constantly check out the ingredients in your favorite foods to make sure your life wasn’t in danger after eating even a tiny bit. For some people with severe food allergies, that’s become their way of life.

Food allergies cause about 30,000 severe allergic reactions and 150 deaths every year in the United States. They affect nearly 4% of adults and about 7% of children under 4 years old. Several studies show that food allergies are becoming more common.

Food allergies occur if your immune system has an abnormal reaction to food. Normally, your immune system protects you from germs and disease by fighting off the harmful organisms that can make you sick. When your immune system makes a mistake and attacks a harmless substance you eat, it can cause serious, even life-threatening, allergic symptoms.

Symptoms of food allergy can include coughing; tingling in the mouth; skin reactions like hives and itching; and nausea, vomiting, stomach pain or diarrhea. Food allergies can also cause a sudden and severe allergic reaction called anaphylaxis. Anaphylaxis brings life-threatening symptoms, which can include difficulty breathing, a drop in blood pressure and narrowing of the airways and wheezing (a whistling sound when you breathe).

Foods that can cause allergies include fish and shellfish such as shrimp, crayfish, lobster and crab; eggs, milk, peanuts, and tree nuts such as walnuts. Peanut and tree nut allergies are the leading causes of anaphylaxis.

Research shows that you’re more likely to develop food allergies if several members of your family have allergies. That includes any type of allergy, including hay fever. If you have 2 allergic parents, you’re more likely to develop food allergy than someone with 1 allergic parent, according to Dr. Dean D. Metcalfe, chief of NIH’s Laboratory of Allergic Diseases in the National Institute of Allergy and Infectious Diseases (NIAID).

“There are many different genes or genetic traits that combine to cause different levels of allergies in some people,” Metcalfe says.

People with asthma are particularly at risk for anaphylactic reactions. “If a child has asthma,” Metcalfe says, “it’s very important for parents to know that their child is at greater risk, because most deaths in children from anaphylaxis to a food occur in children who have asthma.”

Some children are actually born allergic to certain foods, whereas others develop food allergies over time. Children are more likely than adults to outgrow allergies to milk, eggs or soy as their digestive tracts mature and their immune systems develop. They don’t, however, outgrow allergies to peanuts. But scientists are testing whether individuals might be gradually desensitized to peanuts so that eventually they would not suffer an allergic reaction to them.

If you have an allergic reaction to a certain food, you may also be allergic to similar foods. This is called cross-reactivity. For example, if you’re allergic to shrimp, allergy testing may show that you’re also allergic to other seafood.

The only cure for a food allergy is to avoid that particular food. So if you have any unpleasant reaction to food, see your doctor to find out what’s causing the problem. Although many people have bad reactions to certain foods, it may not always be allergy.

Skin tests are the most common tests for allergies like hay fever, but people with food allergies can have serious reactions to skin tests. According to Dr. Daniel Rotrosen, director of NIAID’s Division of Allergy, Immunology and Transplantation, blood tests are a safer method. They’re not always accurate, though, so a positive blood test doesn’t necessarily mean you have an allergy to a particular food.

To help your physician, try to keep a daily diet diary that lists the foods you ate and when you ate them, along with the symptoms you had and when they surfaced. Metcalfe cautions not to overly focus on such food histories, as they can contribute to food phobias and misunderstandings. It’s easy to mistakenly associate things that happen to you with something you’ve eaten hours before. Still, diet diaries can help your doctor decide what allergy tests to give you.

If you have a food allergy, it’s best to prepare for an emergency in case you eat the wrong food by accident.

“When you have an allergic reaction to food,” Rotrosen says, “you may have a good idea of how severe the reaction is, but not always, as it is very difficult to predict.”

Since allergic reactions to food can be hazardous, Rotrosen recommends that people be very cautious. Call 911 if you or someone you know seems to be having an allergic reaction to food.

“Physicians usually prescribe an auto-injector device that has epinephrine (adrenaline) for allergy sufferers,” Rotrosen says. “Unfortunately, too few of these are prescribed, some people do not always carry it with them and some also fail to renew their prescriptions.” Ask your doctor if you need to carry one and learn how to give that shot to yourself if needed.

NIH-supported researchers are working to understand why the immune system sometimes launches attacks against seemingly harmless foods. Researchers are also exploring methods that can lead to quick and accurate diagnosis and treatment of food allergies. Many potential treatments are also under study.

One established treatment for some allergies is called immunotherapy. It involves giving shots under the skin with tiny quantities of extract from the thing you’re allergic to. Giving these injections over a long period can build up your tolerance. For food allergies, however, this procedure can be dangerous. NIH-funded scientists are currently testing various ways of making the approach safer, by modifying the substances themselves or by changing the way they’re introduced into the body.

NIH-funded researchers are also exploring methods to help the immune system dampen allergic reactions and lower your chance of developing food allergies. Researchers hope that a few of the approaches being tested will work and become licensed therapies, giving people with food allergies options other than avoiding the foods they may love.