Breaking Down Oral Allergy Syndrome

The difference between food allergies, food intolerances, and oral allergy symptoms as well as how to manage it

Reactions to foods are common these days. If we don’t have one, we likely know someone who does. Food reactions range from an itchy mouth to intestinal distress or serious but less common, anaphylactic reactions. 

It is not easy to know what causes the reaction or what type it is. It can be confusing because the same food can cause either an allergy or an intolerance. For example, with cow’s milk, people can have an allergic reaction because of the milk proteins (casein and whey), while others may have intestinal cramps, bloating, and gas from the milk carbohydrate (lactose intolerance). Any reaction to food can be lumped into the concept of “food allergy” if the differences are not explained. This blog will explain the differences. 

If you are someone who has food reactions such as an itchy mouth, itchy skin, or even hives from certain fruits or vegetables, then read on to find out more about this type of reactivity. We’ll explain whether these symptoms mean you have oral allergy syndrome and how to manage it. 

What is a Food Allergy? 

Food allergies are immune system reactions triggered by specific proteins in certain foods, resulting in a range of symptoms from mild itching to severe anaphylaxis, which is life-threatening. Symptoms include: 

• Hives 
• Itchiness 
• Swelling of lips, eyes, and/or tongue 
• Nausea  
• Headaches and/or lightheadedness 
• Nasal drip  
• Intestinal pain 
• Brain fog  
• Tiredness 

To diagnose a food allergy, a skin prick or blood test can be performed. A skin prick test involves placing a small amount of the suspected allergen on the skin and pricking the skin underneath. If allergic, a raised bump or redness will develop at the site within 15-20 minutes. A blood test measures immunoglobulin E (IgE), an antibody that initiates and perpetuates an allergic reaction. Blood tests are often used if skin testing can’t be done due to a skin condition, or if it is impractical to do so. 

What is a Food Intolerance? 

Food allergies are not to be confused with food intolerances, which are non-life-threatening reactions to food when the body has trouble digesting certain foods. Reactions occurs when the body doesn’t have enough of a certain enzyme to break down the food, or it might react to certain components of the food. This can lead to symptoms like bloating, stomach pain, or diarrhea. Avoidance of foods that cause these symptoms is often all that is needed to avoid adverse reactions.  

To diagnose a food intolerance, testing can be done using an immunoglobulin G (IgG) test which can be ordered online. However, the evidence is not very strong to support the efficacy of these tests and they can be quite pricey, therefore it’s recommended to simply avoid the foods that may cause discomfort. 

What is Oral Allergy Syndrome? 

Oral Allergy Syndrome (OAS) is the less known type of reaction to food, yet it is highly prevalent. Like a food intolerance, it is not life-threatening and easily managed with simple food preparation. It is a condition in which individuals experience allergic reactions, such as itching or swelling in the mouth, lips, throat, or ears, after consuming certain raw fruits, vegetables, or nuts due to cross-reactivity with pollen allergens. 

Having environmental allergies, commonly known as hay fever, raises the chance of also having OAS. It’s estimated that 30%-75% of people with grass, tree, or fungal allergy also have OAS. The symptoms experienced from OAS can be managed with with antihistamine medications. Learn more about allergies from a Canadian allergist here.  

OAS reactions depend on previous exposure. The body can only react to what it has already suspected to be an enemy invader. This is why a food that has been enjoyed for years can suddenly become a perceived invader. 

Symptoms of Oral Allergy Syndrome 

Symptoms of an oral food allergy are similar to environmental allergies, such as: 

• Itching 
• Tingling or minor swelling of your lips, mouth, tongue, or throat. 
• Bumps on your lips or mouth. 
• Rare symptoms include hives, nausea, itching, redness, or swelling of your skin when you touch certain raw foods. 

To further understand the connection with seasonal allergies, the following are the pollen and food reactivity connections:  

• Birch – apple, apricot, cherry, peach, pear, plum, kiwi, carrot, celery, parsley, peanut, soybean, almond and hazelnut 
• Timothy and Orchard grass– peach, watermelon, orange, tomato and white potato 
• Ragweed– cantaloupe, honeydew, watermelon, banana, cucumber, white potato and zucchini 
• Mugwort – bell pepper, broccoli, cabbage, cauliflower, chard, garlic, onion, parsley, anise, caraway, coriander, fennel and black pepper 

See the full chart of environmental and OAS connections created by Allergy Canada.  

How to Manage OAS 

• Peeling or cooking eliminates the reaction. 
• The allergy irritant in the food is changed by cooking and in digestive juices in the stomach.  
• A person with OAS might react to one or several foods in the same group. 
• Avoidance is the main strategy for managing OAS but not necessary for all foods in the same group. For example, a reaction to apples does not mean a reaction to peaches. 
• Symptoms can be worsened during the season of environmental allergy. For example, apples may cause mouth itch in Spring but not in Winter. 
• Symptoms can be reduced with antihistamine medications. 
• Symptoms can reduced during the winter months when frost destroys pollen and below-freezing temperatures place trees and grass into dormancy. 
• A person can have unknown environmental allergies that become known when OAS is identified. 

Summary of the Different Types of Food Reactions: 

• Allergic reactions are IgG and IgE immune responses to protein molecules in food as it progresses through digestion and can begin in the mouth with itching and progresses to acute body symptoms. Once identified, these foods are to be avoided.  
• Food intolerance reactions are intestinal responses to carbohydrate molecules. Common symptoms are nausea, constipation, diarrhea or gas. Common foods that cause these symptoms are milk, some legumes, grains, fruits or vegetables. 
• Oral Allergy Syndrome is a reaction to elements on the skins of fruits and vegetables that initiate mouth irritation. When peeled, cooked, or digested, these foods are rendered harmless. 

Now you know that if you’ve ‘got the itch’, it might be controllable, understandable, and non-life threatening because it is a symptom of an oral allergy reaction and not a food allergy or food intolerance.  

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