NASET Q & A Corner
Questions and Answers on Food Allergies
What Is Food Allergy?
Food allergy is an abnormal response to a food, triggered by the body’s immune system. There are several types of immune responses to food. The information on this Web site focuses on one type of adverse reaction to food, in which the body produces a specific type of antibody, called immunoglobulin E (IgE).
The binding of IgE antibodies to specific molecules in a food triggers the immune response. Read about what happens during an allergic response to food.
The response may be mild, or in rare cases it can be associated with the severe and life-threatening reaction called anaphylaxis.
If you have a food allergy, it is extremely important for you to work with your healthcare professional to learn what foods cause your allergic reaction. Learn about how healthcare professionals diagnose food allergy.
Sometimes, a reaction to food is not an allergy at all but another type of reaction called food intolerance.
What Is An Allergic Reaction to Food?
A food allergy occurs when the immune system responds to a harmless food as if it were a threat. The first time a person with food allergy is exposed to the food, no symptoms occur. But the body has been now been primed, and when the person eats the food again, an allergic response occurs.
An allergic reaction to food usually takes place within a few minutes to several hours after exposure to the allergen. The process of eating and digesting food and the location of immune cells involved in the allergic reaction process both affect the timing and location of the reaction.
Allergic reaction process
An allergic reaction to food is a two-step process:
Step 1:
The first time you are exposed to a food allergen, your immune system makes specific immunoglobulin E (IgE) antibodies to that allergen. IgE antibodies circulate through your blood and attach to types of immune cells called mast cells and basophils. Mast cells are found in all body tissues, especially in your nose, throat, lungs, skin, and gastrointestinal (GI) tract. Basophils are found in your blood and also in tissues that have become inflamed because of an allergic reaction.
Step 2:
The next time you are exposed to the same food allergen, the allergen binds to the IgE antibodies that are attached to the mast cells and basophils. The binding signals the cells to release massive amounts of chemicals such as histamine.
Depending on the tissue in which they are released, these chemicals will cause you to have various symptoms of food allergy. The symptoms can range from mild to severe. A severe allergic reaction can include a potentially life-threatening reaction called anaphylaxis.
Generally, you are at greater risk for developing a food allergy if you come from a family in which allergies—including food allergies and other allergic diseases such as asthma or eczema—are common. Having two parents who have allergies makes you more likely to develop food allergy than someone with one parent who has allergies.
Symptoms of food allergy
If you are allergic to a particular food, you may experience some or all of the following symptoms:
- Itching in your mouth or swelling
- GI symptoms, such as vomiting, diarrhea, or abdominal cramps and pain
- Hives or eczema
- Tightening of the throat and trouble breathing
- Drop in blood pressure
What Is Anaphylaxis?
If you have a food allergy, there is a chance that you may experience a severe form of allergic reaction known as anaphylaxis. Anaphylaxis may begin suddenly and may lead to death if not immediately treated.
Symptoms
Anaphylaxis includes a wide range of symptoms that can occur in many combinations. Some symptoms are not life-threatening, but the most severe restrict breathing and blood circulation.
Many different parts of your body can be affected:
- Skin—itching, hives, redness, swelling
- Nose—sneezing, stuffy nose, runny nose
- Mouth—itching, swelling of lips or tongue
- Throat—itching, tightness, difficulty swallowing, hoarseness
- Chest—shortness of breath, cough, wheeze, chest pain, tightness
- Heart—weak pulse, passing out, shock
- Gastrointestinal (GI) tract—vomiting, diarrhea, cramps
- Nervous system—dizziness or fainting
How soon after exposure will symptoms occur?
Symptoms may begin within several minutes to several hours after exposure to the food. Sometimes the symptoms go away, only to return two to four hours later or even as many as eight hours later. When you begin to experience symptoms, seek immediate medical attention because anaphylaxis can be life-threatening.
Can anaphylaxis be predicted?
Anaphylaxis caused by an allergic reaction to a certain food is highly unpredictable. The severity of a given attack does not predict the severity of subsequent attacks. The response will vary depending on several factors, such as the following:
- Your sensitivity to the food
- How much of the food you are exposed to
- How the food entered your body
Any anaphylactic reaction may become dangerous and must be evaluated immediately by a healthcare professional.
What can cause anaphylaxis?
Food allergy is the leading cause of anaphylaxis; however, medications, insect stings, and latex can also cause an allergic reaction that leads to anaphylaxis.
How do you know if a person is having an anaphylactic reaction?
Anaphylaxis is highly likely if at least one of the following three conditions occurs:
- Within minutes or several hours of the onset of an illness, a person has skin symptoms (redness, itching, hives) or swollen lips and either difficulty breathing or a drop in blood pressure
- A person was exposed to an allergen likely to cause an allergic reaction and, within minutes or several hours, two or more of the following symptoms occur:
- Skin symptoms or swollen lips
- Difficulty breathing
- A drop in blood pressure
- GI symptoms such as vomiting, diarrhea, or cramping
- A person exposed to an allergen that ispreviouslyknown to cause an allergic reaction in that person experiences a drop in blood pressure.
Is it Food Allergy or Food Intolerance?
Food allergy is sometimes confused with food intolerance.
Lactose intolerance
Lactose is a sugar found in milk and most milk products.Lactase is an enzyme in the lining of the gut that breaks down or digests lactose. Lactose intolerance occurs when lactase is missing. Instead of the enzyme breaking down the sugar, bacteria in the gut break it down, which forms gas, which in turn causes symptoms of bloating, abdominal pain, and sometimes diarrhea.
Lactose intolerance is uncommon in babies and young children under the age of 5 years. Because lactase levels decline as people get older, lactose intolerance becomes more common with age. Lactose intolerance also varies widely based on racial and ethnic background.
Your healthcare professional can use laboratory tests to find out whether your body can digest lactose.
Food additives
Another type of food intolerance is a reaction to certain products that are added to food to enhance taste, add color, or protect against the growth of microbes. Compounds such as monosodium glutamate (MSG) and sulfites are tied to reactions that can be confused with food allergy.
- MSG is a flavor enhancer. When taken in large amounts, it can cause some of the following:
- Flushing
- Sensations of warmth
- Headache
- Chest discomfort
These passing reactions occur rapidly after eating large amounts of food to which MSG has been added.
- Sulfites are found in food for several reasons:
- They have been added to increase crispness or prevent mold growth.
- They occur naturally in the food.
- They have been generated during the winemaking process.
Sulfites can cause breathing problems in people with asthma.
The FDA has banned sulfites as spray-on preservatives for fresh fruits and vegetables. When sulfites are present in foods, they are listed on ingredient labels.
Gluten intolerance
Gluten is a part of wheat, barley, and rye. Gluten intolerance is associated with celiac disease, also called gluten-sensitive enteropathy. This disease develops when the immune system responds abnormally to gluten. This abnormal response does not involve IgE antibody and is not considered a food allergy.
Food poisoning
Some of the symptoms of food allergy, such as abdominal cramping, are common to food poisoning. However, food poisoning is caused by microbes, such as bacteria, and bacterial products, such as toxins, that can contaminate meats and dairy products.
Histamine toxicity
Fish, such as tuna and mackerel that are not refrigerated properly and become contaminated by bacteria, may contain very high levels of histamine. A person who eats such fish may show symptoms that are similar to food allergy. However, this reaction is not a true allergic reaction. Instead, the reaction is called histamine toxicity or scombroid food poisoning.
Other conditions
Several other conditions, such as ulcers and cancers of the gastrointestinal (GI) tract, cause some of the same symptoms as food allergy. These symptoms, which include vomiting, diarrhea, and cramping abdominal pain, become worse when you eat.
