Food Allergy Definition and Facts
Picture of common foods that cause allergies.
- A food allergy is an immune-mediated adverse reaction to a particular food. For someone with a food allergy, eating or swallowing even a tiny amount of a particular food can cause symptoms such as skin rash, nausea, vomiting, cramping, and diarrhea. Because the body is reacting to something that is otherwise harmless, this type of allergic reaction is often called a hypersensitivity reaction. Rarely, a severe allergic reaction can cause a life-threatening set of symptoms called anaphylaxis, or anaphylactic shock.
- Although a large percentage of people believe they have a food allergy, few adults and children, mainly younger than 6 years, have true food allergies. The rest have what is known as food intolerance, an undesirable reaction to a food that does not involve the immune system.
- It is easy to confuse food intolerance with food allergy because they can have similar symptoms. With food intolerance, however, a person usually gets only mild symptoms such as an upset stomach.
- A common example of food intolerance is lactose intolerance, a condition in which a person is missing a certain enzyme necessary to digest dairy proteins. The result is loose stools, gas, and nausea after consuming dairy products such as milk or cheese.
- Another example of food intolerance is reaction to MSG. MSG, or monosodium glutamate, is a white-colored additive used to enhance the flavor of food. It is a fermented mixture of glutamic acid, sodium, and water and is used mainly in Asian cooking. Over the last decades, side effects from MSG have been related to its use in Chinese food and referred to as the Chinese restaurant syndrome. In this syndrome, MSG was suggested as the cause of the symptoms following a Chinese meal. In 1995, a new term was coined, the MSG symptom complex, to include all the reactions that were reported to be related to MSG. These reactions are not a true food allergy, and the exact cause of the reactions is unknown.
What Are the Symptoms and Signs of a Food Allergy?
A person with a food allergy can have symptoms beginning as soon as 2 minutes after eating the food, but reactions may take 1 to 2 hours to appear. Occasionally, symptoms abate quickly, only to recur in 3 to 4 hours.
The most common symptoms include:
- Itching followed by
- A rash of raised, and
- Reddish bumps or wheals
- Lip and mouth swelling
- Belly (stomach) cramps
Other symptoms of food allergies may include:
- Itching and watering in the eyes
- Runny or stuffy nose
Symptoms of a more severe reaction to foods or drinks could include:
- Shortness of breath or difficulty breathing
- Tightness in the chest
- Feeling of tightness or choking in the throat
- Rapid or irregular heart beat
- Feeling dizzy or light-headed
- Losing consciousness
A severe allergic reaction can be life threatening. This severe reaction is referred to as anaphylaxis, or anaphylactic shock. Signs and symptoms of anaphylactic shock are:
- Dizziness, lightheadedness, and loss of consciousness due to dangerously low blood pressure, called "shock."
- An anaphylactic reaction can begin suddenly, or it may develop gradually with itchiness and swelling of the skin and throat and then progress to a severe reaction over a few hours.
- Most people get such a reaction immediately after eating the food, but in a few unusual cases the reaction occurs only after exercising following the ingestion of the food.
- Severe reactions are most often seen with allergies to nuts, fish, and shellfish, although allergy to any food can cause anaphylaxis.
- People with asthma, childhood allergies, eczema, or prior severe food allergies are especially at risk for having an anaphylactic reaction.
MSG reaction can be mistaken for an allergic reaction. Symptoms and signs of MSG reaction include:
- Burning sensation at the back of the neck and radiating down the arms and chest
- Tingling and numbness in the same areas
- Occasionally, difficulty breathing, especially in those with poorly-controlled asthma
- A few people experience seizures, irregular heartbeats, and anaphylaxis after the use of MSG.
Contrary to popular beliefs, MSG has no relation to Alzheimer's or Huntington's disease, or other chronic illnesses.
Allergies can best be described as:
Which Types of Food Trigger Allergic Reactions?
An allergic reaction occurs when the body's immune system overreacts to an allergen, in this case a food protein.
- The white blood cells produce an antibody to this allergen, called immunoglobulin E or IgE.
- When this antibody comes in contact with the particular food protein, it promotes production and release of certain chemicals called "mediators." Histamine is an example of a mediator.
- These mediators act on various parts of the body, mainly the skin, throat, airways, intestines, and heart.
- The effects of the mediators on organs and other cells cause the symptoms of the allergic reaction.
- Any food has the potential to trigger an allergic reaction, but a few foods account for most food allergies. In fact, most food allergies are triggered by one of these eight foods:
- Tree nuts
- Cross-reaction: Generally, people who have allergies react to only a few foods. Occasionally, a person who is allergic to one food also may be allergic to other related foods. This is called cross-reaction. Common examples are:
- Allergy to peanuts - Cross-allergies to soybeans, green beans, and peas
- Allergy to wheat - Cross-allergy to rye
- Allergy to cow's milk - Cross-allergy to goat's milk
- Allergy to pollen - Cross-allergies to foods such as hazelnuts, green apples, peaches, and almonds
- Other allergies: People who have a history of other allergies, such as eczema or asthma, are particularly prone to having a reaction to a food. They are also more likely to have a more severe reaction.
When Should You Call a Doctor for an Allergic Reaction to Food?
If a person experiences symptoms of food allergy, call a health care professional right away for advice.
- He or she may recommend that you go to a hospital emergency department.
- If the person is unable to reach a health care professional and is concerned about their symptoms, they should go to the emergency department.
- Severe reactions, including symptoms such as difficulty breathing, dizziness or lightheadedness, or tightness or choking in the throat, require treatment in an emergency department.
- Even mild symptoms that are not improving or are getting worse require evaluation in an emergency department.
The person should not attempt to drive to the hospital. If no one is available to drive the person immediately, call 9-1-1 for emergency medical transport. While waiting for the ambulance to arrive, start self-treatment.
What Tests Diagnose Food Allergies?
Generally a food allergy is identified by signs and symptoms. Medical professionals are trained to recognize hives, swelling patterns, rashes, and other symptoms associated with allergic reactions.
The person will be asked questions about their medical history and possible triggers of the reaction.
Blood tests and other tests are needed only under very unusual circumstances, such as anaphylaxis.
Some people can pinpoint which food caused the allergic reaction, especially if the reaction occurs within minutes of consuming a particular food. Many others will need to see an allergist for special testing to determine the exact food that is responsible.
For information about allergy shots, see Food Allergy Prevention.
What Natural Home Remedies Treat an Allergic Reaction to Food?
For localized hives or other mild skin reactions:
- Take cool showers or apply cool compresses.
- Wear light clothing that doesn't irritate the skin.
- Take it easy. Keep activity level low.
- To relieve the itching, apply calamine lotion or take over-the-counter antihistamines, such as diphenhydramine (Benadryl) or chlorpheniramine maleate (Chlor-Trimeton).
For all other reactions, especially severe reactions, self-treatment is not recommended. Have a companion drive the person to the hospital emergency department, or call 9-1-1. Here's what to do while waiting for the ambulance:
- Try to stay calm.
- If it's possible to identify the cause of the reaction, prevent further exposure.
- Give the person an antihistamine (1 to 2 tablets or capsules of diphenhydramine [Benadryl]) if they can swallow without difficulty.
- If the person is wheezing or having difficulty breathing, have them use an inhaled bronchodilator such as albuterol (Proventil) or epinephrine (Primatene Mist) if one is available. These inhaled medications dilate the airway.
- If the person is feeling lightheaded or faint, have them lie down and raise their legs higher than their head to help blood flow to the brain.
- If the person has been given an epinephrine kit, they should inject themselves as they have been instructed. The kit provides a premeasured dose of epinephrine, a prescription drug that rapidly reverses the most serious symptoms (see Food Allergy Follow-up).
- Bystanders should administer CPR to a person who becomes unconscious and stops breathing or does not have a pulse.
- If at all possible, the person or their companion should be prepared to tell medical personnel what medications they have taken that day, what they usually take, and their allergy history.
What Is the Medical Treatment for Allergic Reactions to Food?
After getting advice from the health care professional, some mild allergic reactions may be treated at home. Any worsening of symptoms requires medical attention.
- In a severe reaction, the first priority is to protect the airway (breathing) and blood pressure.
- The health care professional will make sure that the airway is open and that the person is getting enough oxygen.
- Oxygen may be given through a tube into the nose or by face mask.
- In severe respiratory distress, mechanical ventilation may be required. A tube is placed in the mouth to keep the airway open.
- In rare cases, a simple surgery is performed to open an airway.
- Blood pressure will be checked frequently.
- An IV line may be started.
- This is used to give saline solution to help boost blood pressure.
- It also may be used to give medication.
The person may need to be admitted to the hospital for further monitoring and treatment.
Could I Be Allergic? Discover Your Allergy Triggers
What Medicine Treats Food Allergies?
The choice of medication and how it is given depends on the severity of the reaction.
- This drug is given only in very severe reactions (anaphylaxis).
- Epinephrine is injected and acts as a bronchodilator (dilates the breathing tubes).
- It also constricts the blood vessels, increasing blood pressure.
- Another medication with similar effects may be given instead.
- For a less severe reaction involving the respiratory tract, an inhaled epinephrine bronchodilator may be used, as in asthma.
- Diphenhydramine (Benadryl)
- This drug reverses the actions of histamine.
- Diphenhydramine is injected when quick action is required.
- It may be given by mouth for a less severe reaction.
- One of these drugs is usually given via IV at first for rapid reversal of the effects of the mediators of the allergic response.
- These drugs should not be confused with the steroids taken by athletes to build muscle and strength.
- These drugs reduce swelling and many other symptoms of allergic reactions.
- The person may need to take an oral corticosteroid for several days after this.
- Oral corticosteroids are often given for less severe reactions.
- A corticosteroid cream or ointment may be used for skin reactions.
- Other medications may be given as needed.
Do You Need to Follow-Up With Your Doctor After Emergency Treatment for a Food Allergy?
Let the person's primary healthcare professional know about the reaction later if he or she was not involved in their treatment.
An allergy specialist (allergist) can determine the difference between true food allergy and food intolerance.
- The allergist will ask about the sequence of events that led to the reaction and record a thorough dietary and medical history.
- He or she may use special tests to find out which food is responsible for the allergic reaction.
- By conducting these tests, the allergist can identify the food responsible for the allergy and help create a plan for avoiding that particular food.
The first step in evaluation for food allergies is testing.
- Skin test: Dilute extracts of various foods are placed on the skin. The allergist looks for the formation of a bump on the skin after 10 to 20 minutes. Swelling at the site of the test can mean that the person is allergic to that particular food.
- Blood test: This may be used to check for antibodies against specific food allergens. These results are confirmed with the oral challenge test in which small doses of the suspected food are given in a mixture of different foods to look for a reaction. If symptoms develop, then the person is proven to have allergies to the particular food.
- Elimination diet: With this test, the person stops eating foods that may be triggers. Gradually these foods are reintroduced back into the diet. The allergist will then be able to pinpoint the allergy-causing food if a reaction occurs.
Individuals with food allergies and their family members should have a clear plan of action in case of an accidental ingestion of the offending food. Emergency medications such as antihistamines and epinephrine should always be available.
- Susceptible people should keep with them an epinephrine kit (a brand name is Epi-Pen Auvi-Q) in case of exposure to the allergen.
- The kit contains a premeasured dose of epinephrine in an easy-to-use syringe for self-injection.
- The person can inject the medicine into their thigh as soon as they feel an allergic reaction coming on.
- Even if the person injects him or herself with epinephrine, they should still proceed immediately to a hospital emergency department.
- It is not unusual for a reaction to abate and then return within a few hours. Even if the person requires no further treatment, they should remain at the hospital until 4 to 6 hours after the beginning of the reaction.
What Is the Prognosis for People With Allergic Reactions to Food?
Most people with food allergies do well if they are able to avoid their trigger foods. With time, many people lose their antibodies to the foods to which they once were allergic to, or "outgrow" the allergy.
- This is most likely to happen if the trigger food is identified and eliminated from the diet.
- This is especially true in children who, by about the age of 10 years, may outgrow their allergies -- mainly to milk and eggs.
- Allergies to nuts, fish, and shellfish can last a lifetime.
Once a person has had a reaction to a food, he or she is more likely to have a severe reaction if exposed to the trigger.
How Can You Prevent Future Triggers to Food Allergies?
The only sure way to prevent future food allergies is to avoid eating a trigger food. Take care because a trigger can be present in many different foods; only a trace amount can cause a reaction.
- Learn to read food labels carefully and know which ingredients to avoid.
- When eating in restaurants, the person should ask what ingredients are in foods they would like to order.
- The person should avoid foods whose ingredients they can't confirm.
- Work with a registered dietitian to plan safe menus.
- Check into special food-allergy cookbooks and groups such as the Food Allergy & Anaphylaxis Network that deal with issues specific to food allergies.
The person should be prepared to deal with an anaphylactic reaction if they are exposed to the culprit food again. If the person has had a severe reaction before, he or she should carry their epinephrine kit.
Never underestimate the danger of an allergic reaction.
Allergy shots and other forms of immunotherapy are being tested in some people who have persistent and disruptive food allergy symptoms.
- The shots do not treat symptoms, but by altering the immune response they prevent future reactions. (This is referred to as immunotherapy.)
- Treatment involves a series of shots, each containing a slightly greater amount of the antigen(s) that cause the reaction.
- Ideally, the person will become "desensitized" to the antigen(s) over time.
- While these are used for allergies to environmental factors such as pollens and insect venoms, their use in food allergies is still under investigation, and they and have not been proven to prevent allergic reactions.
- The effectiveness of shots varies by individual.
Reviewed on 2/28/2020
Sicherer, SH, et al. Food Allergies." Medscape. Feb 05, 2020.