In oral allergy syndrome, the body cross-reacts to certain proteins in specific foods. These proteins are similar to the proteins found in the pollens that are associated with hay fever and seasonal allergies.
As these foods are typically available throughout the year, oral allergy syndrome is not seasonal.
Many food allergies are, in fact, cross-reactions to allergies caused by pollen.
Proteins are found in all organic matter. The immune system identifies specific proteins in order to target bacteria, viruses, and other unwanted germs. However, it sometimes identifies everyday proteins, such as pollens, as harmful as well.
After being eaten or breathed in, these proteins are available in large numbers and the immune system identifies them as abnormal. The body reacts with a significant immune response, which leads to swelling, various other allergy symptoms, and discomfort.
For many, the key signs of oral allergy syndrome are swelling and itchiness of the lips, mouth, tongue, and throat immediately after eating certain fruits and vegetables, especially when raw.
Experts estimate that more than 60 percent of all food allergies are actually cross-reactions to pollen allergies. The most common cause of allergic rhinitis in the United States is birch pollen. However, multiple trees, grasses, and weeds can cause it as well.
Typically, oral allergy syndrome can be traced back to an allergy to the following:
- Japanese cedar
- orchard grass
- Parietaria species
Common foods that cause oral allergy syndrome
As there is a wide range of potential causes of allergic rhinitis, there is also an extremely varied range of fruits and vegetables that cause oral allergy syndrome.
Similarly, different fruits and vegetables may cause a different response depending on the type of pollen the immune system cross-reacts to. According to a paper in the Journal of Allergy, typical foods that may cause a reaction include:
Nuts such as peanuts and walnuts are common allergens and can cause mild to severe symptoms.
- Prunus genus: cherries, nectarines, peaches, plums, apricots
- apples and pears
- Apiaceae family: celery, carrots, parsley, parsnips, cilantro, cumin, dill, chervil, and fennel
- Nightshades: tomatoes, potatoes, and peppers
- Cucurbitaceae family: pumpkins, butternut squashes, zucchini, cucumbers
- hazelnuts and walnuts
- sunflower seeds
Symptoms of oral allergy syndrome only occur after eating specific foods. The symptoms vary significantly, and can peak at different stages of life.
Mild symptoms include:
- itching of the throat, mouth, lips, or tongue
- swelling, particularly of the lips and tongue
More severe symptoms include:
- swelling of the throat
- nausea and vomiting
Additional symptoms can include hives and asthma. Typically, hives occur when the food is being peeled, chopped, or grated. Asthma occurs when the food is being blended or otherwise vaporized, such as during stir-frying.
Those who experience more severe symptoms should see their doctor.
Diagnosing oral allergy syndrome often involves several steps. Typically, these include clinical and laboratory methods.
Clinical methods are the most common. Diagnosis requires confirmation of allergic rhinitis along with itching and tingling that develops after eating fresh fruit or vegetables. In many cases, an accurate patient history shows a link between eating a specific type of food and the start of tingling or swelling.
In other cases, the doctor may propose an elimination diet. The person avoids specific food groups that may cause oral allergy syndrome for a set amount of time and records whether it makes a difference.
A dermatologist can diagnose allergies by using a prick test and measuring the level of reaction.
Laboratory tests typically involve skin testing via a prick test, a scratch test, or a blood test. For skin testing, a dermatologist marks out a grid on the back or the forearm and applies extracts of pollens, fruits, or vegetables. Any marks that develop on the skin are measured after 15 minutes to determine the level of reaction.
If prick tests with the pollen are positive but the food itself fails to provoke a reaction, the person may be asked to eat a certain amount of the suspected food. A reaction immediately after eating this food will confirm the presence of oral allergy syndrome.
In some cases, blood tests might be used to diagnose the condition. First, the doctor performs a test to work out the total level of antibodies in the blood. Another test then checks for specific antibodies. Blood tests are often used when skin tests are not available or practical.
Treatment and lifestyle tips
There are no standard treatments for oral allergy syndrome other than avoiding specific foods that are associated with allergy symptoms. Careful management of diet can ensure that people with the syndrome can lead otherwise normal lives. People with oral allergy syndrome should explain the condition to others to help them understand what foods are off-limits.
In the event of an allergic reaction, initial treatment generally involves rinsing the mouth with water and then resting. Hot drinks can also destroy some proteins, and so inactivate them.
Antihistamines typically take 1-2 hours to work, while the effects of oral allergy syndrome typically start to wear off after about 30 minutes. However, an antihistamine can prevent effects from lingering and should be taken as soon as the reaction occurs.
In some cases, it may be possible to make the immune system less sensitive to the allergen through immunotherapy or allergy shots. This is especially useful when a single allergen is involved. Under-the-skin delivery of immune therapy is currently being studied as a treatment option for oral allergy syndrome.
Does cooking foods help with oral allergy syndrome?
In some cases, cooking foods can destroy the proteins that cause oral allergy syndrome. However, this depends on the foods that trigger the allergies.
In general, nuts and spices are exceptions to the cooking rule. Nuts contain multiple allergens and not all of them are destroyed by heat. The same applies to celery. Allergens in strawberries are also resistant to heat.
Pasteurized fruit juices are generally okay as they have been heat-treated. However, some smoothies may contain raw, unpasteurized juices or purees. These are best avoided if any of the ingredients are triggers.
However, most foods are made sufficiently safe by cooking. Examples include tomatoes, apples, potatoes, pears, and most soft fruits.
In many cases, avoiding the food completely is the only sure way to prevent the symptoms of oral allergy syndrome. However, there are some methods that people may wish to try so they can enjoy their favorite foods.
Lightly microwaving fruits - particularly apples - for about 1 minute and then chilling them immediately may reduce the effects of oral allergy syndrome to a manageable level. This process can remove the main proteins that cause reactions.
In addition, there is usually a large amount of these proteins in the skin, so peeling fruits before consuming them may reduce reactions significantly.
Wearing gloves when peeling fruits can reduce the symptoms of hives. Not stir-frying vegetables can also reduce the risk of asthma.
People with oral allergy syndrome often find that their symptoms worsen during pollen season, so they may wish to avoid trigger foods at the peak of that season.
In addition, managing seasonal allergic rhinitis correctly is key to coping with oral allergy syndrome symptoms. This is normally done with antihistamines and a steroid nasal spray 2 weeks before the season is due to start, and then regular use throughout.