Oral Allergy Syndrome – Signs and symptoms, Treatment

Oral Allergy Syndrome

Also called: OAS


Oral allergy syndrome (OAS) is an allergic reaction to food that involves itchiness, redness and swelling of the mouth after eating certain fruits, vegetables or nuts. The condition is a type of allergic cross-reaction, where the body reacts to one substance after mistaking it for another. The condition occurs as a result of the immune system being unable to distinguish between proteins in pollen (which cause allergies such as hay fever) and similar proteins in some foods.

While OAS and a nut allergy are both types of an allergic response that can occur from nuts, the two are not the same. Symptoms are usually different, and an individual can have both conditions, or one or the other. However, a person must have an allergy to pollen (even a very mild one) in order to be affected by OAS.

OAS only causes a reaction when fresh fruits, vegetables or nuts are consumed. Because the proteins in these foods are temperature sensitive, heating or freezing these foods often makes them far less allergenic. An individual may be more sensitive to OAS during those seasons when problem pollen allergens are in the air.

OAS is usually not a severe condition, and medical treatment is rarely necessary. Symptoms usually include only slight discomfort that lasts for a matter of minutes. However, more sensitive individuals can react with gastrointestinal symptoms (e.g., nausea, diarrhea) or, in extreme cases, with the life-threatening condition known as anaphylactic shock. Reactions can also trigger asthma attacks in individuals with asthma.

Antihistamines are commonly used to treat the symptoms associated with OAS. These drugs are capable of disrupting the processes of the allergic reaction and lessening symptoms.

Allergy shots are also effectively used as a preventative treatment against OAS. This type of immunotherapy involves regular injections that build up a patient’s resistance to certain allergens. Patients with OAS who receive allergy shots for pollen proteins usually find their reactions to fruits, vegetables and nuts subside as well. However, allergy shots are intended to work for pollen allergies, not food allergies.

About oral allergy syndrome

Oral allergy syndrome (OAS) is an allergic reaction to fruits, vegetables and nuts caused by an individual’s similar allergy to pollen (small, powdery grains that are the fertilizing element of flowering plants, much of which can easily become airborne). The cross-reaction between the two is the result of similarities in proteins found in some types of pollen and in some fruits, vegetables and nuts. Also known as pollen-food syndrome, the reaction causes itching and swelling in the mouth, throat and lips when a certain fruit, vegetable or nut is consumed.

OAS is always cross-reactive. A nut allergy is not the same as oral allergy syndrome. However, an individual who is allergic to nuts may also have an OAS cross-reaction when eating some nuts. While both are allergic reactions, OAS and a nut allergy will often result in different symptoms.

Individuals with OAS must first suffer from hay fever (allergic rhinitis) or a similar pollen allergy. Because of the similarities between the proteins in different types of foods, this type of cross-reactivity is possible. With a pollen allergy, a person’s immune system has been sensitized to the allergen pollen. When the immune system encounters a food protein resembling the pollen protein to which it is sensitive, it triggers the allergic cascade.

Because people with pollen allergies tend to be more sensitive to pollen during the seasons when it is present in the air, OAS reactions can be stronger during this period. This time period can vary depending on the type of pollen allergy.

OAS results in itching or swelling around the mouth, lips, tongue or throat. This occurs as the fruits, vegetables or nuts are consumed and their proteins come into contact with these local areas. Some of the proteins are absorbed through the lining of the mouth and trigger the immune system to release certain chemicals that cause localized allergy symptoms. The chemicals cause the cells in the lining of the mouth and throat to swell, resulting in inflammation. Individuals may also develop symptoms from simply handling raw fruit and vegetables.

This type of allergic reaction is based on superficial contact, and the fruit, vegetable and nut proteins are not absorbed into the blood and circulated throughout the body in great quantity. This usually produces only mild symptoms. Typically, OAS symptoms cause mild discomfort for only for a few minutes before subsiding.

In some rare individuals, gastrointestinal symptoms occur after the problem fruit, vegetable or nut has passed into the digestive tract. Nausea, diarrhea and an upset stomach may all result in these individuals.

While an OAS reaction is usually mild, highly sensitive people can experience life-threatening anaphylactic shock.  This condition is characterized by a constriction of the airways that makes breathing difficult. OAS can also trigger an asthma attack in sensitive individuals.

Only fresh fruits, vegetables and nuts can cause OAS. Because their proteins are so temperature-sensitive, these foods are often less likely to cause an OAS reaction after being canned or boiled. Some allergic individuals also find that frozen fruits and vegetables do not cause an allergic reaction. Nuts, however, may trigger a reaction whether raw or cooked.

Types and differences

There are several different types of fresh fruits, vegetables and nuts that may result in cross-reaction in individuals with pollenallergies. The type of fruit, vegetable or nut often depends on the type of pollen allergy. Allergen and fruit, vegetable and nut cross-reactions include:

Type of
Potential cross reactions
Birch tree pollenalmonds, apples, apricots, carrots, celery, cherries, coriander, fennel, hazelnuts, kiwi, nectarines, parsley, parsnips, peach, pears, peppers, plums, potatoes, prunes, walnuts
Grass pollencelery, melon (watermelon), oranges, peaches, tomatoes
Ragweed pollenbananas, melons (watermelon, cantaloupe, honeydew), gourd family (cucumber, zucchini and squash)
Alder pollencelery, pears, apples, almonds, cherries, hazelnuts, peaches, parsley
Mugwort pollencelery, fennel, carrots, parsley, coriander sunflower, peppers

People with ragweed pollen allergies may also experience a cross-reaction when consuming sunflower seeds, echinacea or chamomile tea.

Signs and symptoms of oral allergy syndrome

The symptoms of oral allergy syndrome (OAS) are generally centered around the lips, mouth or pharynx (back of the throat). Symptoms include:

  • Swelling of the lips, tongue, throat or palate (upper surface of the mouth)

  • Itching of the lips, mouth or pharynx

  • Gingivitis (gum disease)

These symptoms typically develop immediately after the problem food is consumed. Patients may also develop watery, itchy eyes, a runny nose, sneezing, conjunctivitis (inflammation of the tissue lining the inside of the eyelid) and rhinitis (inflammation of the mucous membrane that lines the nose).

Though more rare, some individuals will experience allergy symptoms as the body attempts to expel the food. These gastrointestinal symptoms include:

  • Stomach cramping
  • Nausea
  • Vomiting
  • Diarrhea

Occasionally some individuals will have a more serious response as a result of OAS. Though very rare, this reaction may include:

  • Asthma attack. Onset of asthma symptoms, including:

    • Rapid breathing
    • Chest pain or tightness
    • Chronic coughing
    • Breathing difficulty
    • Fever
    • Headache
    • Stuffy head

  • Anaphylaxis. Potentially life-threatening reaction characterized by constricted airways. Symptoms may include:

    • Shortness of breath
    • Tightening in the chest or throat
    • Choking
    • Loss of consciousness

Symptoms may also develop from simply handling raw fresh fruits and vegetables. Contact with the peels or juice of problem foods may lead to a rash or itching and swelling on the skin. Sneezing, runny nose and watery eyes may also result from touching the foods.

Diagnosis methods for OAS

To successfully diagnose an oral allergy syndrome (OAS) in an individual, a physician will start with a physical examination and a review of the patient’s medical history. A history of allergies – particularly pollen allergies – can help a physician determine whether an oral allergy is present.

While an allergic reaction to pollen is a requirement for anyone suffering from OAS, some people may have such slight pollen reactions that they fail to recognize the condition. In these individuals it is often useful to conduct a skin test. This test involves pricking, scratching or injecting food or pollen extracts into the patient’s skin. The skin will react with redness and swelling for those extracts capable of eliciting an allergic reaction. Skin testing is not 100 percent accurate, however, and results will vary depending on the extract being tested. In addition, skin testing may not be performed in patients with severe allergic reactions.

An elimination diet is sometimes used to verify whether an individual is allergic to a particular fruit, vegetable or nut. This treatment involves removing the foods in question from a patient’s diet to see if the allergic reactions persist. This trial-and-error approach often takes weeks for results, but it can be effective at pinpointing a problem food.

Some other types of allergy tests, including oral challenge tests, are not used in the diagnosis of OAS.

Treatment and prevention of OAS

The best way to prevent the symptoms associated with oral allergy syndrome (OAS) is to avoid any offending foods. By successfully removing foods that cross-react with an individual’s pollen allergy, a person can prevent any further cross-reactions. It is often possible to substantially reduce or prevent the allergic nature of some types of fruits and vegetables simply by cooking them. Fortunately, the problem protein found in these types of foods is very sensitive to changes in temperature. Frozen fruits and vegetables often loose their ability to stimulate the symptoms of OAS, as do canned and dried foods. Nuts, however, may trigger allergic reactions whether raw or cooked.

The symptoms of OAS are typically mild, and individuals with the condition usually do not require medical treatment. However, antihistamines can be used to relieve symptoms when a reaction to a fruit, vegetable or nut occurs. It should be noted that antihistamines should only be used to treat OAS if a physician has determined that a food allergy is not also present. Antihistamines are not a replacement for epinephrine in the case of a food allergy.

Antihistamines are medications that provide relief for more common allergy reactions such as hives, sneezing, runny nose and gastrointestinal symptoms. Antihistamines directly counteract the effects of the histamines, which are responsible for most allergy symptoms. This type of medication can successfully treat the itching and swelling associated with OAS. Antihistamines can also be taken prior to contact with a fruit, vegetable or nut to lessen the severity of a reaction.

Allergy shots have been proven effective at treating OAS. This type of immunotherapy involves the patient receiving regular injections of a problem protein to build up a tolerance. Since OAS symptoms are caused by a cross reaction, allergy shots that effectively treat a pollen allergy will also affect any cross-reactions with similar food proteins.

The treatment of pollen allergies does not change in individuals who have OAS.

Questions for your doctor

Preparing questions in advance can help patients to have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions regarding oral allergy syndrome:

  1. Do my symptoms indicate oral allergy syndrome?
  2. What methods will you use to determine if I have oral allergy syndrome?
  3. Does oral allergy syndrome pose a danger to my overall health?
  4. What foods are most likely to cause me to have a reaction?
  5. Am I equally as likely to have a reaction to frozen, canned or cooked fruits and vegetables?
  6. Is it safe to touch the foods, as long as I don’t consume them?
  7. Am I more likely to develop oral allergy syndrome at certain times of year?
  8. What are my treatment options?
  9. Can I continue to eat problematic foods if I take medication beforehand?
  10. I am allergic to pollen. What are my odds of developing oral allergy syndrome?
  11. Will oral allergy syndrome have an effect on my asthma?
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