Oral Allergy Syndrome topples peanut allergy in the 'league tables'

Nutritionist Micki Rose investigates

I was stunned to read in an online BBC news report recently that allergy to fruit and vegetables is set to top peanut allergy in the UK. Allergy clinics are reporting significant increases in the number of cases of oral allergy syndrome (OAS) they’re seeing. They say there are more severe cases than there were before, and that the condition is starting earlier than it did.

In the report, the University Hospital of Wales, for example, reported a five-fold increase in cases, and Dr Pamela Ewan from Addenbrookes Hospital in Cambridge warned of the explosion of cases: ‘It’s a bit like the peanut allergy epidemic of the 1990s. I think fruit and vegetables are becoming the epidemic now. In terms of numbers, fruit and vegetables are the new form of peanut allergy.’ Allergy to fruit and veg: I thought they were supposed to be healthy! So, what’s going on?

What is OAS?
A true IgE-mediated allergy, OAS is more accurately termed ‘pollen-food syndrome’ by some experts. Simply put, it is a condition where the body becomes sensitised to pollen and then develops an allergy to foods that have a similar protein structure. Basically, the body becomes confused and reacts to what should be healthy foods. The most common allergy is to birch pollen and a subsequent sensitivity to structurally similar apples and hazelnuts. At a recent allergy conference in Vienna, these two foods were named by allergists from all over the world as the two most prevalent allergens in adults and children over three years old. Sunflower seed allergy is also coming up a lot and some experts warn that the reactions to the seed can be even more severe than those to peanut.

It’s estimated that up to 40% of all pollen (hayfever) sufferers will develop OAS at some point. The foods affected will depend on the type of pollens they are sensitive to. Researchers have been working on trying to discover the proteins involved so they can better predict what foods a specific hay fever sufferer is likely to react to. It seems it is a bit like shifting sand, though, as there is no guarantee that a pollen allergy will develop at all into OAS. Some evidence exists that people who never even knew they had a pollen problem can develop OAS out of the blue. Also, new foods and pollens can be triggered at any time. See the section below on cross-reactions and food families, although this can only be considered as a general guide.

The good news is that OAS is very unlikely to develop into a full blown food allergy with a risk of anaphylaxis, and that symptoms are mainly mild and temporary, although there are reports that the problem is becoming more severe. Dr Ewan in the BBC report again: ‘Early on when we first picked it up, it was passed off as not being serious. It began with fairly mild itching in the mouth. But now we are seeing people who are getting really severe throat closure, a significant swelling at the back of the throat that can impede breathing.’

I also note that a person can apparently have both a nut anaphylaxis problem and a nut OAS problem. It makes me wonder, perhaps, how many of those suspected of nut allergy are in fact suffering with OAS? It would be interesting to research.

OAS symptoms
The usual symptoms of OAS are normally mild and in the mouth, throat, ears and nose. The foods rarely upset anywhere in the digestive system further down than the stomach, and this is probably because the stomach acid breaks them down sufficiently. There have been studies, though, which suggest that certain of the proteins involved may be linked to IBS and skin problems such as eczema and urticaria. More of this later.

The most common symptom of OAS is a tingling or itchy feeling in the mouth after eating raw fruit and veg. Symptoms can also include itching, swelling or redness of the mouth, lips, gums, tongue or throat, itchy ears, rhinitis, conjunctivitis and hoarseness.

The uvula, the dangly bit at the back of your throat, can swell, as can your oesophagus, pharynx or windpipe causing more serious throat closure and consequent breathing difficulties.

Symptoms can come on immediately after eating or, for the most sensitive, touching or inhaling usually raw fruit and vegetables, spices, herbs, nuts and seeds. The problem is not seasonal as it can occur all year round, but the body tends to be more reactive during the pollen season and slightly afterwards.

OAS usually starts in teenage or young adulthood, but allergy clinics are reporting a change. Dr Adam Fox at the Guy’s and St Thomas’ hospital in London, in the BBC report is quoted as saying: ‘Normally we would see this among young adults as they start to develop hayfever but we are seeing much more of it among young children.’

This is not good news, and suggests something is going on to encourage more cases, more severe symptoms and is starting at an earlier age.

In the House of Lords Science and Technology Committee Allergy Report for 2006/7, Professor William Cookson from Imperial College, London said that developing an allergy depended on both genetic and environmental factors. Professor Adnan Custovic, professor of allergy at the University of Manchester, doubted that the genetics of our population had changed enough in the past fifty years for there to be a genetic explanation for such a rise and that it must therefore be environmental.

Committee suggestions
The committee asked the government to consider several possible causes of allergy including the hygiene hypothesis (protective effects of early childhood infection, bowel flora, farming techniques and our ever-closer proximity to animals), changes in our diet, and greater exposure to allergens, atmospheric pollution and tobacco smoke. They specifically asked the government to consider researching the effects of ventilation, humidity, mite reduction and the role chemicals used in the construction industry, presumably in the building of houses, might have.

They also called for a deeper consideration of the link between air quality, climate change and human health. In other words, is it an increase in our indoor and outdoor pollution that is causing problems like OAS to rise and affect us younger?

Air and plant
Experts do know from research that exposure to diesel can potentiate any existing and latent allergens when that allergen, like pollen, comes into contact with the body along with diesel particles. It has been shown that people exposed to diesel fumes and pollen have a much stronger reaction than they do to the pollen alone. This makes the increase in allergies generally, but OAS especially, more understandable given the huge increase in diesel and other chemical use over the past fifty years.

We also know that some of the antigens, such as bet v 1 in birch and the apple antigen Mal d 1, are made by plants when they are under environmental stress and, very possibly the level of the allergen is increased by environmental pollution. This, of course, also means that plants that have this ability are valuable crops as they are the most likely to be successful in our polluted atmosphere. In other words, there are more of the plants around through natural and man-made selection and they are making more of the antigens to cope with our environment. No wonder more people are reacting.

Personally, I would also have to add the lowering of the nutrition in our diet and the lack of minerals, particularly zinc, in the soils in which our food is grown as a factor.

And what about the huge number of agrochemicals on our food – could that be an issue? And what about the way our foods are stored? We mustn’t forget that bacteria and moulds also have their own protein structure and that some of these have been linked to allergy. This may be why ripe and older food seem to cause more of an OAS reaction.

OAS diagnosis can be straightforward: if the person has a pollen allergy and displays
typical oral symptoms that are repeated with the same food challenges, they are normally diagnosed with OAS. It can be confirmed with RAST (skin prick) testing although some experts prefer to use prick-to-prick testing, where the food itself is pricked and then transferred to the skin of the patient because test substances in vials may not be good enough quality. It’s important to get a diagnosis as OAS is rarely life-threatening (although throat closure can of course affect breathing) whereas a food allergy can develop into anaphylaxis.

Here’s the technical bit about proteins and antigens, so bear with me. It seems that the foods people may become sensitive to do not necessarily come from the same botanical families; it is more to do with similar proteins and similar receptor sites. There are several proteins involved and research is ongoing, but a couple of well-known ones are profilins, regulatory proteins involved in reproduction, hence the link to pollen, and lipid transfer proteins (LTP) which are found in a huge number of plants and help to defend them against pathogens.

An example: the most common cross-reaction is between birch pollen and apples.
Apple flesh contains a lot of an allergenic protein called Mal d 1, which is structurally very similar to the Bet v 1 protein in birch pollen.

Apple skin contains a different protein, Mal d 3, so some people who peel apples won’t react to them at all. That is unless they happen also to have developed a sensitisation to the Pru p 3 protein in peaches which is very similar to the Mal d 3.

Bit of a nightmare, isn’t it? That’s why many people can develop new trigger foods over the years, although some people won’t ever react, and foods can contain several of the different types of protein too so you could be reacting to more than one protein in the food.

Look at the table to see which pollens are believed to be linked to which food at the moment. Alternatively, check the AllFam database which lists the most up-to-date cross-reactions that have been found for each type of protein. It seems that the majority of allergens in fruit and veg involve only four out the thousands of proteins and animal food allergens involve just three. So, by typing ‘plants’ or ‘animals’ into the search, you get a list of all the proteins involved, and by clicking on each protein, a list of the foods linked to it. So, if you know what pollen you are sensitive to, you can check what proteins in foods could be a problem and check out each of those foods to see if you’re OK.

Of course, just because you have that pollen sensitivity, doesn’t mean you will be sensitive to the foods with similar protein structures, nor does it mean that just because you are sensitive to one of those foods in the list, that you will be sensitive to others. If you do develop a sensitivity to a new food, you can check out what protein is involved and what other foods are on the list.

It’s a bit complicated, I’m afraid, but the information is there now, which could be really helpful for managing OAS. Indeed, it might even be a good idea to rotate the various foods so you don’t have them too often and are therefore less likely, one would think, to develop future problems. We do know a cumulative load is likely to be part of the problem.

One important recent finding to note is that there appears to be a possible link between birch pollen cross-reactive foods and skin conditions such as eczema and urticaria, as well as IBS. The proteins are different to the ones that cause the oral symptoms it seems, but it has been shown that removing apples and other birch pollen-linked foods from the diet of sufferers of these conditions has led to real improvement.

My initial thought would be that if IgE reactions were found to other pollens, then removing the known cross-reactive foods from the diet might also help, even if removing birch pollen foods doesn’t. An interesting thought for those with seemingly unsolvable IBS and skin cases.

Managing OAS
Apart from knowing a bit more about what foods and proteins are involved, what else can you do to limit OAS?

• Get a diagnosis, then avoid the foods you know you react to, and possibly rotate the foods in that same group to avoid developing future issues.

• If you have a reaction, swill a liquid antihistamine around your mouth.

• Most reactions are caused by raw foods whereas cooking them can destroy some of the offending proteins, which is why some people can’t eat a raw apple, but are fine with cooked. Unfortunately, the LTPs mentioned above are heat stable and resistant to stomach acid so tend to cause more problems even when food is cooked.

• Experiment with cooking your offending foods, peel them or choose frozen, dried, canned, pasteurised or otherwise processed versions to see if that helps. One point though, if you react to raw celery, nuts, seeds or spices, it seems that cooking doesn’t help so be extra careful. Similarly, if you react to non-OAS foods such as egg, nut or shrimp, get this checked out further as it may not be OAS. If you’re very sensitive, avoid touching or inhaling the offending food. And remember, sometimes food that’s been stored a long time is more reactive than fresh.

• Since pollen is the key, and we know symptoms are worse during and slightly after the pollen season, if you have serious OAS can you structure your life so you spend most of the season near the sea where there’s less pollen, in a different part of the country, or abroad, perhaps? There’s an excuse for a villa in the sunshine…! The Midlands is said to have less birch pollen and you might be able to limit your exposure in the UK with the knowledge that pollen seasons generally start earlier in the south and later in Scotland. Note also that pollen seasons are thought to be starting earlier now because of climate change.

• Make sure you have sufficient stomach acid. We know that symptoms tend to occur in the body above the stomach because the proteins are broken down in the acid there. Stomach acid often lowers after our forties and when under stress, so get checked out by a nutritionist and top it up if need be.

• Improve your immunity. It’s not inevitable that you will develop other trigger foods, especially if you look after yourself well. Regular quercetin, nature’s antihistamine, may help as will keeping your vitamin, mineral and fatty acid levels nice and balanced. OAS is a mix between a person’s immune response and exposure to an allergen, so improving the first and limiting the second seems like a good idea.

• Since we believe air pollution may also be a factor, it would make equal sense to invest in a HEPA air filter, a vacuum with a pollen filter and live as far away from polluted areas, such as major roads, as possible.

In summary, it seems that OAS is becoming more prevalent because of our increased exposure to air pollution and the natural survival of plants able to cope with that pollution. I also reckon our immune systems could do with a bit of an overhaul. There is a lot we can do to limit our own exposure to air pollution, especially inside our own homes, such as chucking out the air fresheners (my pet hate!), controlling dust mites, better ventilation and limiting pollen exposure with HEPA filters and the like, as discussed above.

Either way, it’s worrying. I always thought fruit and veg were the healthiest foods we could eat, but it seems not for everyone. Perhaps we are just learning to adapt to our new chemical age like the plants – we should perhaps be taking a leaf (pun intended) out of their book by adapting and strengthening our bodies to suit.

Pollen-Food Cross-reactions

Hazel (February– April)
Hazel nuts.

Alder (Feb–April)
Celery, pear, cherry, parsley, apple, almond, hazel nut, peach.

Birch (March–May)
Apple, apricot, spinach, cherry, plum, prune, kiwi, carrot, potato, pepper, fennel, parsley, nectarine, coriander, parsnip, pear, hazelnut, almond, wheat, buckwheat, peanut, walnut, peach, celery.

Pine (April–May)

Grass (May–July)
Peach, tomato, melon, orange, swiss chard, wheat, celery.

Pellitory (June– September)
Cherry, melon.

Ragweed (June–September)
Melon, banana, dandelion, sunflower, courgette, camomile, cucumber.

Mugwort (July– September)
Celery, melon, apple, peanut, spices, kiwi, parsley, sunflower, fennel, carrot, parsley, camomile, coriander, sweet pepper.

1.Concern in rise over allergies
2. Food Allergies get curiouser and curiouser
3. House of Lords report on allergy
4. Government response to the report
5. *Radauer C, Bublin M, Wagner S, Mari A, Breiteneder H:
Allergens are distributed into few protein families and possess a restricted number of biochemical functions. J Allergy Clin Immunol 2008, 121, 847-52.
6. The Complete Guide to Food Allergy and Intolerance, 4th edition, Professor Jonathan Brostoff and Linda Gamlin.
7. Vickerstaff Health Services – OAS
8. Wikipedia
9. Ragweed and OAS– AAAAI
10. Alex Gazzola - OAS
11. Current Allergy & ClinicaI Immunology, June 2009 Vol 22, No 2. Oral Allergy Syndrome – What’s New?, Harry Steinman MB, ChB, DCh(SA)

First published in 2009

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