Oral allergy syndrome, or OAS, is a condition that’s thought to affect around 10% of the nation. Sufferers experience allergic symptoms after eating certain foods that contain pollen proteins similar to the ones that cause their hayfever.

In the simplest sense, OAS is somewhere between hayfever and a food allergy (although its symptoms are generally less severe than a food allergy). Plant based foods such as fruits and vegetables (particularly raw), nuts, seeds, herbs and spices can all cause the symptoms of oral allergy syndrome.


What Are the Symptoms of Oral Allergy Syndrome?

The symptoms usually affect the mouth first, but can spread to the throat, nose and eyes. They normally start to occur just minutes or even seconds after eating a trigger food. Symptoms include:

  • Tingly, swollen lips
  • Tingling, itching, burning and swelling of the mouth, soft palate and tongue
  • Scratchy throat
  • Itchy inner ears
  • Itchy, watery eyes
  • Runny nose
  • Sneezing
  • Hives (red, raised, itchy bumps on the skin similar to nettle rash)
  • A worsening of asthma symptoms

Symptoms should start to subside 20 minutes or so after the trigger food has been removed from the mouth. (It’s advised that you spit trigger foods out if you start to notice a response.)

In very rare cases, oral allergy syndrome can cause a severe allergic reaction, breathing difficulties and anaphylactic shock.


What Causes Oral Allergy Syndrome?

If the pollen of certain trees and grasses causes you to suffer the symptoms of hayfever, you have more chance of also having oral allergy syndrome.

It’s thought that those with an allergic hayfever response to silver birch pollen will have OAS. Having an allergy to rubber can also trigger OAS.

OAS is all down to a phenomenon called cross reactivity. All pollen contains proteins and some of these proteins are responsible for causing hayfever in certain people. If you’re sensitive to these proteins, when you breathe in the pollen from certain trees and grasses, you’ll experience the annoying symptoms of hayfever.

Unfortunately, the pollen of certain plant based foods also contains proteins that are very similar to the proteins that cause hayfever. The immune system cannot tell the difference between them, so consuming these foods will cause the symptoms of OAS. This is a so-called cross reactivity reaction.

When the immune system detects a protein you’re allergic to, called an allergen, it releases antibodies which then trigger the release of histamine. Histamine is responsible for allergic symptoms such as watery eyes, a runny nose and swollen lips. Hence anti-histamine drugs are usually given to help stop hayfever.

For example, silver birch pollen contains a protein very similar to that of apples, nectarines, apricots, carrots, potatoes, tomatoes, celery, almonds, walnuts and parsley. If silver birch trees cause you to suffer hayfever, it is possible you’ll experience OAS after eating one or more of these foods, but not everyone does.

Being allergic to rubber (which is a natural product harvested from trees) can mean that eating avocadoes, bananas, peppers, tomatoes and peanuts can trigger OAS.

See Allergic Living for a full cross-reactivity chart.

Oral allergy syndrome is different and less serious than a food allergy to say celery or peanuts.


Managing Oral Allergy Syndrome

Cooking fruits and vegetables will denature the offending proteins, meaning that they’re less likely to cause OAS symptoms.

You can test for certain allergens, and some you may already know about. Avoiding your trigger foods and always reading food labels is key to managing your symptoms. We wish you a (relatively) allergy free season!

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