Overview
A food allergy is an immune system reaction to certain foods. Even a tiny amount of an allergy-causing food can trigger symptoms such as itching, rashes, upset stomach and wheezing. In some people, a food allergy can cause a life-threatening reaction known as anaphylaxis.
Food allergy affects an estimated 10% of the general population and about 8% of children.
Treatment plans include education to avoid allergy-causing foods. Medicines can help lessen symptoms or prevent reactions to accidental exposure. Life-saving medicine is needed if a person experiences anaphylaxis.
A food allergy is different from food intolerance. Both conditions may have similar digestive symptoms. But a food intolerance is not an immune system reaction. Instead, this condition happens when the body can't digest certain foods or use certain nutrients.
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Symptoms
Food allergy symptoms usually start within a few minutes to two hours after eating the allergy-causing food. The seriousness of symptoms can vary widely. The symptoms may range from mild to life-threatening.
The most common food allergy symptoms include:
- A rash, itchiness, raised patches on the skin or swollen skin.
- Itching or swelling of the lips, face, tongue and throat.
- Watery, itchy or swollen eyes.
- Belly pain, upset stomach, diarrhea or vomiting.
- Stuffy or runny nose.
- Wheezing, coughing or trouble breathing.
- Dizziness, lightheadedness or fainting.
Anaphylaxis
A food allergy can trigger a severe allergic reaction called anaphylaxis. This can cause life-threatening signs and symptoms, including:
- Tightening of the airways.
- A swollen throat or the sensation of a lump in your throat that makes it hard to breathe.
- A drop in blood pressure.
- Rapid pulse.
- Confusion or other changes in mental status.
- Dizziness, lightheadedness or loss of consciousness.
Emergency treatment is critical for anaphylaxis. Untreated, anaphylaxis can be fatal.
When to see a doctor
See a healthcare professional or allergist if you have food allergy symptoms shortly after eating. If possible, see a health professional when the allergic reaction is occurring. This can help with a diagnosis.
Get emergency care if you have signs or symptoms of anaphylaxis.
Causes
A food allergy happens when the immune system reacts to food as if it were reacting to a germ or parasite. The immune system creates antibodies to a certain protein in a food item, such as a peanut.
If a person is allergic to peanuts, the antibodies in the blood find and attach themselves to these peanut proteins. This antibody activity sends a signal for the immune system to mount an attack. The signs and symptoms of a food allergy are the result of the immune system fighting what it thinks is a foreign substance.
A food that causes an allergic reaction is called an allergen. The most common food allergens include:
- Cow's milk.
- Chicken eggs.
- Peanuts.
- Tree nuts, such as walnuts and pecans.
- Shellfish, such as shrimp, lobster, scallops and crab.
- Fish.
- Wheat.
- Soy.
Pollen-food allergy syndrome
People who are allergic to certain pollens may be allergic to certain raw plant foods. But people usually have no reaction if the food is cooked or processed. This condition is called pollen-food allergy syndrome or oral allergy syndrome. The following plant allergens are linked to possible food allergies.
Birch pollen. If you are allergic to birch pollen, you also may have a reaction to several foods.
Fruits
- Apple
- Apricot
- Cherry
- Peach
- Pear
- Plum
Nuts and legumes
- Almond
- Hazelnut
- Peanut
- Soybean
Herbs and seeds
- Aniseed
- Caraway seed
- Coriander
- Fennel
- Parsley
Vegetables
Ragweed pollen. If you are allergic to ragweed pollen, you also may have a reaction to some foods.
- Banana
- Cantaloupe
- Cucumber
- Honeydew
- Watermelon
- Zucchini
Grass pollens. If you are allergic to grass pollens, you also may be allergic to several foods.
Fruits
- Cantaloupe
- Honeydew
- Kiwi
- Orange
- Tomato
- Watermelon
Legumes
Vegetables
Mugwort pollen. If you are allergic to mugwort pollen, you also may be allergic to several foods:
Fruits
- Bell pepper
- Grape
- Peach
- Lychee
- Mango
Herbs and seeds
- Aniseed
- Black pepper
- Caraway seed
- Coriander
- Fennel
- Paprika
- Mustard
- Parsley
- Sunflower seeds
Vegetables
- Broccoli
- Cabbage
- Carrot
- Cauliflower
- Celery
- Garlic
- Onion
Exercise-induced food anaphylaxis
Some people may experience an anaphylactic allergic reaction if they do moderate or strenuous exercise a few hours after eating certain foods. Most commonly this happens after eating wheat or shellfish. If these people don't exercise after eating the allergen, they don't have an allergic reaction.
Other reactions
Other reactions to food may have symptoms similar to food allergies, but activities in the body other than immune system reactions are involved.
Food intolerance is when the body cannot digest certain foods or break down nutrients in foods. A food intolerance may cause digestive symptoms similar to allergic reactions:
- Excessive gas.
- Bloating.
- Cramping or stomach pain.
- Diarrhea.
Examples of food intolerance include:
- Lactose intolerance is the result of the body not being able to break down the main sugar in milk called lactose.
- Gluten sensitivity is the result of the body not being able to break down a protein called gluten that is in wheat, barley and rye.
Food poisoning is a sickness people get from something they ate or drank. The causes are germs or other substances in the food or drink. Symptoms most often start within hours or days of eating the food.
Sensitivity to additives in certain foods can cause symptoms similar to allergic reactions. For example, sulfites used to preserve dried fruit, canned goods and wine can trigger asthma attacks in people with severe asthma.
Celiac disease is an immune system reaction to gluten, but it's a unique reaction that's different from a typical food allergy. It does not cause anaphylaxis. The immune system reaction to gluten causes damage to the small intestine and leads to an inability to absorb certain nutrients.
Risk factors
Food allergy risk factors include:
- Family history. Having a family member with any allergy is a key risk factor for food allergies.
- Other allergies. An allergy to one food increases the risk of becoming allergic to another food. Having other allergies, such as hay fever, also increases the risk of food allergies.
- Age. Food allergies commonly begin during childhood, especially during the infant and toddler years. Children typically outgrow allergies to milk, soy, wheat and eggs. Severe food allergies and allergies to peanuts, tree nuts and shellfish are more likely to be lifelong.
- Atopic dermatitis. Atopic dermatitis, also called eczema, is a condition that causes dry and itchy skin, rashes, thickened skin, and other symptoms. Having this condition in early childhood increases the risk of having food allergies.
- Asthma. Asthma and food allergy commonly occur together. When they do, both food allergy and asthma symptoms are more likely to be severe.
Prevention
Introducing peanut products and eggs early in childhood may lower the risk of allergy to peanuts and eggs. Studies have shown that introducing these foods in the diet of children 4 to 11 months of age lessens the likelihood of having peanut and egg allergies later. Studies of early introduction of other common food allergens have not shown that this lowers risk.
Before introducing common allergy-related foods, talk with your child's healthcare team about the best time to offer them.
Children with pets or who grow up around livestock on a farm may have a lower risk of food allergies.