The return of sunny days does not mean relief for everyone. For allergy sufferers, this is often the start of problems: the emission of pollen causes multiple inconveniences (tight throat, runny nose, stinging eyes, etc.) which can even be accompanied by a reaction to certain fruits. But why is a person allergic to birch pollen more likely to be allergic to pear or peach? And how can we free ourselves from this cross-allergy (or at least live with it better)? Practical advice from Dr Sebastien Lefèvre, head of the allergology department at CHR Metz-Thionville.
Similar proteins that “trick” the immune system
Having itchy eyes and a scratchy throat after taking a walk or eating an apple: such is the daily life of many French people suffering from “cross allergies”. A phenomenon well known to Dr Sebastien Lefèvre, head of the allergology department at CHR Metz-Thionville.
“In the northern region of Lyon, where birch pollen is very present, many residents develop fruit allergies. In fact, birch protein (PR-10) is also found in many raw fruits and vegetables,” confides the allergist.
Result ? In around 50 to 70% of cases of pollen allergy (most often birch, but hazel, alder or cypress are also affected), affected people can develop a sensitivity to several fruits – such as apple, pear, peach, or even walnuts. The reason: the similarity of proteins between these foods and pollen, which “deceives” the immune system.
It may therefore be possible to suffer from a joint allergy to cypress pollen, citrus fruits and peach, as the Pasteur Institute points out.
“In the South of France, another type of cross allergy dominates: linked to LTP (lipid transfer proteins), which are found in particular in apricots, peaches, and even in certain drugs such as cannabis… with the result being allergic rhinitis and reactions to fruits, such as citrus fruits”, specifies the expert.
Important detail: these famous temperature-sensitive proteins are destroyed by heat. “This is why the symptoms, often localized to the mouth and throat (itching, tingling, etc.), appear especially when raw foods are consumed. This phenomenon is called oral allergy syndrome. further reveals Dr Sebastien Lefèvre.
Allergies that multiply… because of “environmental stress”
If the number of cases of cross allergy “has tripled in the space of 25 years” according to Professor Jocelyne Just, pneumo-allergist at the American Hospital in Paris, this phenomenon can be explained.
“PR-10 is a “defense” protein that plants produce in greater quantities when they are subjected to environmental stress (drought, floods, climate change). Fruits from organic farming also contain more of it, because they are more exposed to external attacks: micro-organisms – fungi, bacteria, etc. – will settle on flowers and fruits and make them “stress”, says the head of the allergology center at CHR Metz-Thionville.
Reason why we now speak of environmental disease, “because these allergies are largely linked to factors that we experience: pollution, climate, diet”, continues the expert.
Fruits are not the only foods at risk of cross allergies… Certain products, such as plant-based milks very rich in PR-10, can also pose a problem: “not being chewed, they arrive directly in the stomach without being broken down, which can cause significant reactions. They are therefore generally not recommended for sensitive people. warns the doctor.
Cross allergies: how to get rid of them?
Faced with this delicate question, Dr Sebastien Lefèvre plays the sincerity card.“Desensitization to pollen can help: in a third of cases, it improves cross-allergies but remains without any effect in another third and can unfortunately aggravate them in the remaining third,” warns the allergist.
No miracle solution therefore on paper, although progressive reintroduction protocols exist: “for example, they consist of eating cooked apples over several weeks (12 in total), then slowly reintroducing raw apples. This method allows you to develop a “tolerance” to love, and not a desensitization.”
Indeed, to maintain this tolerance, patients must continue to regularly consume the foods concerned. Otherwise, the allergy may return. “We are therefore unable to cure these patients at present.“, confirms the doctor.
However, certain easy habits to adopt can reduce allergic reactions.
“I recommend peeling the fruit and heating it for 15 seconds in the microwave, since the PR-10 protein is heat-sensitive,” recommends the expert.“But above all, it is absolutely essential to consult an allergist to establish an accurate diagnosis and avoid risks,” he concludes.