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Allergies to the pollen of trees and plants are common. But sometimes those allergies can progress and cause a reaction to eating particular raw fruits, vegetables, nuts and legumes.

As the days get longer, the grass starts growing and blossom appears on trees, it’s easy to be filled with the joys of spring. But for some, it’s also when the all-too-familiar itchy eyes and runny nose returns. Hay fever is back – and just the sound of a nearby lawnmower is enough to bring on a sneeze or two. Just to add to their frustrations, hay fever sufferers may find they develop surprising food allergies alongside their sniffles.

Pollen food syndrome (also known as oral allergy syndrome) is perhaps more common than you’d think. While 20 percent of the UK are reported to be at some point in their life, two percent of the UK population are also affected by the related food syndrome.

So, what causes it? What foods are you likely to be allergic to and how can you treat it?

Why would hay fever lead to food allergies?

When someone has hay fever, their body is having an IgE-mediated allergy. “IgE is an antibody that normally we produce, to fight parasitic infections like malaria. And for some reasons, people can develop them to things like pollen and get hay fever,” explains Manchester University’s Professor Clare Mills.

The problem is, some foods have proteins which are very similar to those in pollen, and when some people with hay fever consume them – especially when they’re raw – their bodies effectively think they’re ingesting pollen. Amena Warner is head of clinical services at the charity, AllergyUK and explains: “The fault is with the immune system which defends itself by having an allergic reaction."

What are the symptoms?

People with pollen food allergy can expect swelling and itching inside the mouth, throat and ears. This will happen shortly after consuming the food. For most people, the symptoms are mild and will pass relatively quickly (especially with the aid of an antihistamine). However, for an unfortunate few, symptoms can go further. “In some cases, it causes very severe reactions,” says Warner, highlighting that this could include breathing difficulties. Thankfully, this is relatively rare.

If you have hay fever are there other factors that could lead to you developing allergies to ingredients? Mills is currently carrying out research examining the – including the onset of pollen-related food allergies. Mills explains they tend to impact adults more than children. “Whether that's because you have to have been around for a certain length of time to kind of be exposed to the differences in pollens, we’re not sure yet, but it's often something people start developing in their 20s-40s.

“They are largely – not exclusively – but largely, related to having an allergy to pollen of trees like birch and alder. There is a molecule in fruit particularly, that is a lookalike of a molecule in the pollen that causes hay fever. Many years ago, in Sweden, they found that something like 70 percent of people who had birch pollen allergy also would react to eating fresh apples.”

However, it’s not just the individual but what they are exposed to. Mills explains: “We showed in a study that the level of that molecule increases in apples that have been stored in a modified atmosphere. One of the nice things about this type of storage is it enables us to eat apples in March, which we wouldn't ordinarily be able to do, but unfortunately, they have much higher levels of this allergen.”

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This depends on the type of pollen you’re allergic to, though generally speaking it's raw fruit, vegetables, legumes and nuts. AllergyUK have a detailing the pollens together with the foods that can cause a reaction. They are:

Tree pollen: Apple, apricot, cherry, coriander, kiwi, nectarine, parsley, peach, pear, plum, strawberry, celery, bean sprouts, carrot, mangetout, green pepper, potato, soya, tomato, parsnip, peas, basil, coriander, fennel, oregano, parsley, paprika, pepper, thyme.

Grass pollen: Kiwi, melon, orange, watermelon, date, potato, swiss chard, tomato, wheat, peas, peanut.

Weed pollen: Apple, melon, orange, peach, tomato, watermelon, celery, carrot, green pepper, onion, sunflower seed, aniseed, celery salt, mustard, spices, coriander, fennel, parsley.

Not sure what type of pollen you’re allergic to? That probably comes down to when you are allergic, if it’s March – late May it’s likely to be tree pollen, if it’s May – July than grass pollen and if it’s June – September weed pollen. Of course, you could be allergic to more than one type of pollen, there is a cross over during these periods and environmental factors can alter the dates – for example if it’s a particularly wet/dry spring.

“While we all know that there are people who have anaphylactic reactions to peanuts, not so many know that some people have the same response to peaches,” explains Mills. “This is something we’ve seen in the Mediterranean area. In fact British people who may spend a large proportion of their year in Spain can get this kind of allergy and in some instances, they won't just react to peach but they'll react to other fruits and vegetables - everything from lettuce and cabbage to peaches, apricots, plums and cherries… They can give severe reactions which aren’t removed by cooking.”

Like peanuts, if you have an allergic response to peaches you need to take it seriously. While for many it will be due to pollen food syndrome, for an unlucky few it won't and could have .

If you think you have pollen food syndrome

“If anybody has severe allergic reactions to food, they must go and get it sorted out,” says Warner, matter-of-factly. “You must seek advice from a healthcare professional who will conduct tests.”

Warner warns though that you shouldn’t be tempted to pay for unregulated tests: “There are a lot of tests you can have done through the internet where you might send a hair sample and you get 500 allergens tested, but many are unvalidated… They relieve people from a lot of their money, but it won't give the important information that they need on how to deal with their allergy and it puts them at risk.”

This is a view backed up by the who explain: "There are also many commercially available tests that claim to diagnose food hypersensitivity. You should avoid these because they have no scientific basis. They can be harmful when multiple foods are excluded without reason, or if they are not reintroduced under guidance of a dietitian."

Originally published April 2022