Although, compared to many of the more serious allergies, the symptoms of oral allergy syndrome are relatively mild, it can still be debilitating. Alex Gazzola, whose new book, Living with Food Allergy has just come out, has researched the syndrome in some detail.

Oral allergy syndrome (OAS) is a usually mild allergy to raw fruits, vegetables, spices, herbs, seeds and nuts, the symptoms of which are generally restricted to the mouth – typically intense itching, tingling, reddening or even mild swelling on the lips and tongue following consumption of the culprit foods. The throat and gums may also be irritated.

If as a hay fever sufferer you’re sensitised to the proteins in pollens, reactions to plant-based foods may later develop because similar proteins are widely distributed in the botanical kingdom. Your immune system, ‘thinking’ you’ve taken a mouthful of pollen, reacts.

Trigger pollens and foods

Most OAS is caused by allergy to birch pollen, which is prevalent in spring (March/April), especially across Scotland, northern and southern England (central regions have much less). Birch pollen allergy affects up to 4% of the population, most of whom also have associated mild food allergies – even out of pollen season. The potentially reactive foods are many and varied, and include avocado, the nightshades (pepper, potato, tomato), the stone fruits (peach, plum, apricot, cherry), kiwi, spinach and many nuts, herbs and spices. Apples and members of the carrot family (carrots, parsley, celery, celeriac, parsnip) are especially troublesome.

Those with grass pollen allergy – that is, summer hay fever – are unlikely to suffer from associated food allergies, though some do react to tomato, gluten grains, melons, nuts, potato and Swiss chard.

Those with weed pollen allergy – provoking autumn hay fever – may react to apple, banana, members of the carrot family, the daisy family (camomile, sunflower), the melon family (melons, courgette, cucumber) and some spices.

Is it OAS?

While researching my book, Living with Food Allergy, I was greatly struck by the lack of awareness of this increasing problem.

One allergy sufferer in her thirties I spoke with had been experiencing unpleasant oral allergies to carrots and apples for fifteen years, and mostly avoided these foods. Having moved regularly during that time, she’d had five doctors. Not one of these GPs could tell her why she was reacting, even though responses to raw apples and carrot are strongly indicative of birch-pollen allergy.

I suggested that she must suffer heavily rom spring hay fever. ‘Terribly,’ came the reply. ‘How did you know?’ She was stunned to learn of the link, and greatly reassured that the reactions were unlikely to ever be or become serious, although I urged her to speak again with her doctor and seek a referral for confirmation.

Importance of diagnosis

Even if you strongly suspect OAS, a diagnosis is key. It usually takes the form of skin-prick testing (with fresh raw extracts of suspected foods) and a clinical history of reactions. Testing for specific pollens can also be carried out. With this information, a consultant can not only diagnose OAS, but more importantly distinguish between OAS and a classical (non pollen-related) food allergy. This can be vital, because food allergy related to OAS is unlikely to cause severe reactions or anaphylaxis, while other food allergies may well require you to take stricter precautions or carry adrenaline.

Nuts, peanuts and OAS?

This is especially important when nuts are involved, as it is possible to have a classic nut or peanut allergy, and have a separate OAS-related nut response too. Specialist allergy dietitian Isabel Skypala relates the unusual case of a birch-pollen allergy sufferer who’d been safely consuming roasted peanuts for most of his adult life. On trying some unfamiliar and exotic raw peanuts for the first time, however, he suffered a severe reaction which required hospitalisation – the result of an allergy to a relatively newly discovered peanut allergen (ara h 8), which is destroyed by roasting and which shares similar characteristics to birch pollen allergen.

Everyone is different, and the unpredictability of nut or peanut reactions is such that you must seek specialist advice.

So what can I eat?

Sadly, some people – typically those who react to a number of raw foods – avoid virtually all fruits and vegetables, even those to which they do not react, just to ‘play safe’. Others may do this largely subconsciously, gravitating towards a diet heavy in meats, fish and dairy products, and very low in plant foods, which they somehow feel may not ‘agree’ with them, not even realising they have food allergies. This is a pity, as food restrictions can compromise nutrition and deny enjoyment of delicious wholesome foods. It is also usually unnecessary. Each individual has his or her own set of trigger foods, and you need only avoid those to which you react.

Cooked or raw?

Furthermore, cooked, tinned or microwaved foods are usually safe – as heat or processing destroys the fragile allergens typically involved in OAS. Pasteurised fruit juices are fine too. The possible exceptions to the ‘cooked is OK’ rule are celery, nuts, seeds and spices.

Which is better?

Generally, and the possible exceptions aside, it’s sensible to continue to eat cooked versions of foods to which you react. Many view raw vegetables as superior nutritionally, but this is not always the case. Cooked tomatoes and carrots, for instance, contain much more bioavailable quantities of lycopene and betacarotene than their raw counterparts.

True, vitamin C is vulnerable to heat, but it is easy to get enough from safe raw foods, such as citrus fruits and grapes, which most can tolerate.

Ripeness

There appears to be a link between the ripeness of a fruit and the severity of any response; some people with OAS to apple may be able to enjoy ‘just picked’ apples safely, for instance.

Peeling apples – and other foods – may reduce or eliminate the reaction too. Isabel Skypala points out that some breeds are more reactive, including Golden Delicious, Granny Smiths, Braeburn and Cox’s Orange. For OAS sufferers who miss raw apples, she also suggests cautiously experimenting with micro-waving apples for a minute or less, then refrigerating them to bring them back to room temperature.

Salads

Many salad leaves can be involved in OAS, including lettuce, dandelion and endive (daisy family), rocket and watercress (mustard family) and young spinach and chard (goosefoot family).

Lamb’s lettuce, which is in none of these families, appears friendly to OAS sufferers; it is available bagged in stores such as M&S and Waitrose.

New triggers

Be aware that most people with OAS regularly encounter new triggers. A friend of mine, a birch-pollen allergy sufferer with associated food allergies only recently discovered additional reactions to dill (a member of the carrot family) and to lightly steamed asparagus. Accordingly, be on your guard and take precautions: rinsing your mouth with water and taking oral anti-histamines should relieve an unexpected reaction within half an hour.

Urticaria and asthma

Finally, be aware that merely preparing fruit and vegetables – peeling or chopping them, for example – can trigger mild urticaria in the hands, and that close proximity to cooking vegetables (especially stir-frying) can cause respiratory symptoms as allergens are vaporised and inhaled.

The outlook

Pollen-related OAS is rare in children, but more frequent in older teenagers and young adults. It often improves in middle-age. There is no cure, although those with severe pollen allergies who receive immunotherapy do find that associated food allergies improve considerably.

Alex Gazzola's books on food allergy, food intolerance and coeliac disease, are all available from Amazon and other bookshops.

First published in 2006

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