All we need to know about food allergies: Facts and myths


What is a Food allergies? There Are Different Types of Allergic Reactions to Foods

If your child has symptoms after eating certain foods, he or she may have a food allergy.

A food allergy occurs when the body’s immune system sees a certain food as harmful and reacts by causing symptoms. This is an allergic reaction. Foods that cause allergic reactions are allergens.

Two Categories of Food Allergies

  1. Immunoglobulin E (IgE) mediated. Symptoms result from the body’s immune system making antibodies called Immunoglobulin E (IgE) antibodies. These IgE antibodies react with a certain food.
  2. Non-IgE mediated. Other parts of the body’s immune system react to a certain food. This reaction causes symptoms, but does not involve an IgE antibody. Someone can have both IgE mediated and non-IgE mediated food allergies.

IgE Mediated Food Allergies

The IgE mediated food allergies most common in infants and children are eggs, milk, peanuts, tree nuts, soy and wheat. The allergic reaction can involve the skin, mouth, eyes, lungs, heart, gut and brain. Some of the symptoms can include:

  • Skin rash, itching, hives
  • Swelling of the lips, tongue or throat
  • Shortness of breath, trouble breathing, wheezing
  • Stomach pain, vomiting, diarrhea
  • Feeling like something awful is about to happen
Food allergies

Sometimes allergy symptoms are mild. Other times they can be severe. Take all allergic symptoms seriously. Mild and severe symptoms can lead to a serious allergic reaction called anaphylaxis (anna-fih-LACK-sis). This reaction usually involves more than one part of the body and can get worse fast. Anaphylaxis must be treated right away to provide the best chance for improvement and prevent serious, potentially life-threatening complications.

Treat anaphylaxis with epinephrine. This medicine is safe and comes in an easy-to-use device called an auto-injector. You can’t rely on antihistamines to treat anaphylaxis. The symptoms of an anaphylactic reaction occur shortly after contact with an allergen. In some individuals, there may be a delay of two to three hours before symptoms first appear.

Cross-Reactivity and Oral Allergy Syndrome

Having an IgE mediated allergy to one food can mean your child is allergic to similar foods. For example, if your child is allergic to shrimp, he or she may be allergic to other types of shellfish, such as crab or crayfish. Or if your child is allergic to cow’s milk, he or she may also be allergic to goat’s and sheep’s milk. The reaction between different foods is called cross-reactivity. This happens when proteins in one food are similar to the proteins in another food.

Cross-reactivity also can occur between latex and certain foods. For example, a child who has an allergy to latex may also have an allergy to bananas, avocados, kiwis or chestnuts.

Some people who have allergies to pollens, such as ragweed and grasses, may also be allergic to some foods. Proteins in the pollens are like the proteins in some fruits and vegetables. So, if your child is allergic to ragweed, he or she may have an allergic reaction to melons and bananas. That’s because the protein in ragweed looks like the proteins in melons and bananas. This condition is oral allergy syndrome.

Symptoms of an oral allergy syndrome include an itchy mouth, throat or tongue. Symptoms can be more severe and may include hives, shortness of breath and vomiting. Reactions usually occur only when someone eats raw food. In rare cases, reactions can be life-threatening and need epinephrine.

Non-IgE Mediated Food Allergies

Most symptoms of non-IgE mediated food allergies involve the digestive tract. Symptoms may be vomiting and diarrhea. The symptoms can take longer to develop and may last longer than IgE mediated allergy symptoms. Sometimes, a reaction to a food allergen occurs up 3 days after eating the food allergen.

When an allergic reaction occurs with this type of allergy, epinephrine is usually not needed. In general, the best way to treat these allergies is to stay away from the food that causes the reaction. Below are examples of conditions related to non-IgE mediated food allergies.

Eosinophilic Esophagitis (EoE)

Eosinophilic (ee-uh-sin-uh-fil-ik) esophagitis is an inflamed esophagus. The esophagus is a tube from the throat to the stomach. An allergy to a food can cause this condition.

With EoE, swallowing food can be hard and painful. Symptoms in infants and toddlers are irritability, problems with eating and poor weight gain. Older children may have reflux, vomiting, stomach pain, chest pain and a feeling like food is “stuck” in their throat. The symptoms can occur days or even weeks after eating a food allergen.

EoE is treated by special diets that remove the foods that are causing the condition. Medication may also be used to reduce inflammation.

Food Protein-Induced Enterocolitis Syndrome (FPIES)

FPIES is another type of food allergy. It most often affects young infants. Symptoms usually don’t appear for two or more hours. Symptoms include vomiting, which starts about 2 hours or later after eating the food causing the condition. This condition can also cause diarrhea and failure to gain weight or height. Once the infant stops eating the food causing the allergy, the symptoms go away.

Rarely, severe vomiting and diarrhea can occur which can lead to dehydration and even shock. Shock occurs when the body is not getting enough blood flow. Emergency treatment for severe symptoms must occur right away at a hospital. The foods most likely to cause a reaction are dairy, soy, rice, oat, barley, green beans, peas, sweet potatoes, squash and poultry.

Allergic Proctocolitis

Allergic proctocolitis is an allergy to formula or breast milk. This condition inflames the lower part of the intestine. It affects infants in their first year of life and usually ends by age 1 year.

The symptoms include blood-streaked, watery and mucus-filled stools. Infants may also develop green stools, diarrhea, vomiting, anemia (low blood count) and fussiness. When properly diagnosed, symptoms resolve once the offending food(s) are removed from the diet.

If Allergic to One Food, Do You Have to Avoid Related Foods?

A food allergy occurs when the immune system overreacts to a food. The most common type is when the immune system makes a type of antibody called IgE to proteins in a particular food. This is an IgE-mediated food allergy. When exposure to the food occurs, symptoms start quickly. Symptoms include any or several of the following: skin itching, hives, swelling of the skin, nausea, vomiting, diarrhea, breathing difficulty (wheezing, repeated throat clearing, cough, throat tightness), or anaphylaxis.

Anaphylaxis is a severe allergic reaction that is rapid in onset and progressive. Symptoms of anaphylaxis involve more than one organ system from the above list. They can also include dizziness or loss of consciousness (from a drop in blood pressure) and other serious, potentially life-threatening complications. Anaphylaxis can occur with any IgE-mediated food allergy.

The most common food allergens are milk, egg, wheat, soy, peanut, tree nuts, fish and shellfish.

Cross-reactivity occurs when the proteins in one substance are like the proteins in another. As a result, the immune system sees them as the same. In the case of food allergies, cross-reactivity can occur between one food and another. Cross-reactivity can also happen between pollen and foods or latex and foods.

Because of cross-reactivity, testing and diagnosis of food allergies can be challenging. Since the immune system sees the similar proteins as the same, a positive skin test or blood test (serum IgE) can result for a food, yet the patient may be actually allergic to a substance that is cross-reactive to that food.

However, the individual may or may not have any allergic symptoms from eating that food. The individual may not have allergic symptoms from a food that is cross-reactive with another food or pollen to which the individual is allergic. This is true even though they have a positive skin test or blood test to that food. This point cannot be emphasized enough. Many people end up avoiding foods because of a positive test and in some cases, they may have been eating that food before without any problems.

Cross-Reactivity between Cow’s Milk and Milk from Other Mammals

There is a high degree of cross-reactivity between cow’s milk and the milk from other mammals such as goat and sheep. In studies, the risk of allergy (resulting in symptoms) to goat’s milk or sheep’s milk in a person with cow’s milk allergy is about 90%.

The risk is much lower, about 5%, for allergy to mare’s milk (or donkey’s milk) which is less cross-reactive with cow’s milk.

Cross-Reactivity between Foods in the Same Animal Group

Cross-reactivity is uncommon between foods in the same animal group. For example, most people with an allergy to cow’s milk can eat beef and most people with an allergy to egg can eat chicken without any symptoms to the respective meats.

Cross-Reactivity between Peanut and Other Legumes (Soy and Beans)

Peanuts and soybean are in the legume family, which includes beans and lentils. A common question that comes up for people with an allergy to peanut is whether they can eat soy-based foods or other beans. More than 50% of peanut-allergic individuals will have a positive skin test or blood allergy test to another legume (soy, other beans) but it turns out that 95% of them can tolerate and eat the cross-reactive legumes. Many years ago, it was common to recommend avoidance of legumes, including soy, because of a peanut allergy but this practice has been proven unnecessary.

Cross-Reactivity between Peanut and Tree Nuts or Seeds

As noted above, peanuts are legumes and are not related to tree nuts (almonds, walnuts, cashews, etc.). However, about 35% of peanut-allergic toddlers in the U.S. have or will develop a tree nut allergy. It is fairly common to be “co-allergic” to tree nuts if a child is peanut allergic. Doctors thus recommend that young children avoid tree nuts if they are peanut-allergic. Safety is also a concern. Young children may have a hard time distinguishing a tree nut from a peanut. Thus, there is the potential of cross-contamination of tree nut products with peanut.

Studies have investigated whether the common occurrence of allergy to both peanut and tree nuts is due to allergen cross-reactivity. At least one study revealed that there MAY be some cross-reactive parts of the allergic proteins in common. But true cross-reactivity is unknown. However, the larger issue is that allergy to tree nuts is common in peanut allergic individuals. Doctors should watch for tree nut allergy in peanut-allergic individuals. Their recommendations should be made on an individual basis.

The same hold for peanut allergy and allergy to seeds such as sesame seed. There are a few individuals who are allergic to both. This is likely due to the occurrence of more than one food allergy in highly allergic individuals rather than cross-reactivity. With respect to tree nuts, there is high degree of cross-reactivity between cashew and pistachio and between walnut and pecan. Most people who are allergic to one tree nut are not allergic to all tree nuts.

Cross-Reactivity between Fish

There is a lot of cross-reactivity among different species of fish including fresh and salt water fish. The risk of allergy to other fish when an individual is allergic to one fish is about 50%.

Cross-Reactivity between Shellfish

Shellfish, like fish, peanuts, and tree nuts are commonly associated with severe, potentially life-threatening reactions. There is a high degree of cross-reactivity among the crustacean shellfish (shrimp, lobster, crab, crawfish).

The risk of allergy to another crustacean shellfish is 75%. The risk may be lower for cross-reactivity between crustacean shellfish and non-crustacean shellfish (mollusks) such as clam, oyster, scallop, mussels. Of note, there is cross-reactivity between chitins (a component of exoskeleton of shellfish and insects) in dust mites and crustacean shellfish. This can result in “false positive” testing for shellfish without any clinical symptoms.

Cross-Reactivity between Pollen and Foods (Pollen-Food Syndrome or Oral Allergy Syndrome)

Some individuals with pollen allergies (allergic rhinitis or hay fever) can develop symptoms around and in the mouth and throat immediately after eating raw fresh fruits, vegetables, nuts or seeds that contain proteins cross-reactive to the pollen. This is known as oral allergy syndrome or pollen-food syndrome. For example, people with birch pollen allergy may experience symptoms after eating raw apples, peaches, pitted fruits, carrot, peanut and hazelnut among others. Likewise, ragweed allergic individuals experience symptoms with melons among other foods.

Symptoms can include itching or tingling of the lips, tongue, and roof of the mouth or throat. In addition, there may be hives around the mouth area where the food came into contact with the skin or swelling of the lips, tongue, and throat tightness. In less than 3%, symptoms may become systemic (beyond the mouth or throat) or result in anaphylaxis.

Cooked forms of the foods are usually tolerated because the food proteins which are pollen cross-reactive are fragile and are broken down when subjected to heat or stomach acids (so, for example, raw apples can cause symptoms but an apple pie can be eaten without any symptoms). Not all people with pollen allergies have oral allergy syndrome (OAS), but many do. And, for those who do have oral allergy syndrome, they may experience symptoms with some but not all foods cross-reactive to a particular pollen to which they are allergic.

Cross-Reactivity between Latex and Foods

Latex is a natural product that is derived from the milky substance extracted from a rubber tree. Common natural rubber latex products include latex gloves and balloons. Latex can cause several types of allergic or non-allergic (irritant) reactions. The most concerning type is an IgE-mediated allergic reaction to latex that results in immediate reactions such hives, swelling, wheezing, and anaphylaxis. About 30 to 50% of people with IgE-mediated allergies to latex can experience symptoms with any or several fruits cross-reactive to latex including most commonly banana, avocado, kiwi, and chestnut. However, the overall prevalence of IgE-mediated reactions to latex is rare. Most reported reactions are due to contact sensitivity.

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