Peach is a stone fruit belonging to the Rosaceae family of fruits. This family comprises many of the most widely consumed fruits in the western countries such as apple, pear, strawberry, and the stone fruits apricot, plum and cherry. These fruits are the foods most frequently involved in food allergic reactions in adolescents and adults in Europe. Females are affected twice as frequently as males. Apple allergy is the most frequent food allergy in Central and Northern Europe in areas rich of birch trees, whereas peach is the food most frequently involved in allergic reactions in the Mediterranean area in countries such as Spain, Italy and Israel.
Most of the patients allergic to peach notice itching of mouth and throat, and itching, redness and swelling of the lips, within the 5-15 minutes after eating the fruit, or even while chewing and swallowing it. These symptoms relapse 15 to 60 minutes later. This is known as the “oral allergy syndrome”. Some patients present more serious reactions after peach intake, preceded or not by the mouth symptoms, and with a variable involvement of the skin, the stomach and nose or lungs, and/or anaphylaxis. In the skin involvement patients develop wheals (urticaria) with or without swelling (angioedema). When present, swelling most frequently affects face, lips, and eyelids. In the stomach patients may experience burning or pain, cramps, vomiting, and/or diarrhoea. The nose and lungs are less frequently involved, and patients present with itching of the nose, sneezing, and watery discharge (hayfever or rhinitis) and/or cough, chest tightness, wheezing and short breath (asthma). Some peach allergic patients may develop generalised reactions with involvement of the skin together with other organs. These generalised allergic reactions are known as anaphylaxis, and are a medical emergency. Fortunately, only a minority of patients with anaphylaxis present a decrease in blood pressure (hypotension). This is the most severe and life threatening allergic reaction known as anaphylactic shock. Other life threatening reactions such as severe asthma attack or glottis oedema are exceptionally observed.
Related foods (cross reactivity)
There are regional differences in the manifestations of peach allergy within Europe. In North and Central Europe peach allergy is observed in patients allergic to birch pollen. These subjects generally have other plant food allergies involving Rosaceae fruits (apple being the most frequently associated), nuts (especially hazelnut), and vegetables (mainly celery and carrot). All these plant food allergies linked to birch pollen allergy have similar symptoms and development. The food allergy is a consequence of birch pollen allergy: patients first become allergic to some proteins (allergens) of birch pollen, and they secondary react to similar allergens present in the foods (cross-reactivity phenomenon). The most important allergens are easily destroyed by cooking and the digestion process (labile allergens), and thus can only induce local contact reactions in the mouth and throat where they are still intact. This explains why oral symptoms are for most of the patients the unique manifestation of this food allergy, and why reactions are only induced by fresh peach; commercial peach juices, peach in syrup, or peach jam are generally well tolerated.
However, in Southern Europe – Spain and Italy – and Israel, in areas without birch trees, peach allergy is more severe. The majority of patients have symptoms from the mouth, but generalised reactions such as hives (urticaria) and anaphylaxis appear in more than 1/3 of patients. All the patients react to fresh peach, when it is eaten with the peel, whereas some of them can tolerate the ingestion of the peeled fruit. Foods containing processed peach commonly induce allergic reactions. A frequent (>50%) and characteristic complaint in these patients is the appearance of wheals in hands, forearms, face and neck when handling or peeling raw peaches, due to the contact with the fruit peel. For some patients this is the first manifestation of peach allergy, and sometimes the only one since it prevents them from eating peaches.
The severity and the special characteristics of peach allergy in the Mediterranean area are related to one particular protein that is the most important allergen for South European patients. Since this allergen resists the digestion processes, it can induce local contact reactions in skin, mouth and throat, as well as reactions in distant organs after it has been taken up by body. Its resistance to high temperature explains the reactivity of patients to processed peach foods, and its abundance in the peel of the fruit explains the special reactivity to peach peel.
Who, when, how long, and how often?
Since all the people eating peach are exposed to its lipid transfer protein, why does only the Mediterranean population get sensitised to this allergen? This puzzling question is not yet answered. Differences in the genetic background, in dietary habits or in pollen exposure could be on the basis. Whether the exposure to some local pollens such as those of plane tree or mugwort may favour this fruit allergy is currently under investigation.
Peach allergy is suspected on the basis of the medical history which establish the relationship between the contact with the fruit and the appearance of symptoms, it is supported by the demonstration of allergy antibodies by means of skin and blood tests, and it is confirmed by an oral challenge.
The best test to demonstrate a reaction to peach is the prick-prick test with fresh peach. In this test the lancet is plunged several times into the fruit immediately before pricking the patient’s skin with it. The frequency of positive results in allergic patients is high, generally over 90%. Peel and pulp can be tested separately. False negative skin tests are frequently found with commercial peach extracts, especially in patients sensitised to labile peach allergens which can be modified during the extract preparation. This factor can also reduce the diagnostic performance of the commercially available blood tests.
In the clinical practice it is rarely indispensable to make oral challenges to confirm the clinical suspicion if the symptoms are unequivocal (which is almost always the case), and the patient presents specific IgE to peach. In those patients with anaphylaxis in whom specific IgE is demonstrated, oral challenges should not be performed.
The only recommendation to peach allergic patients is the strict avoidance of the fruit. This is especially important in those patients from the Mediterranean area sensitised to lipid transfer protein who are at risk of severe reactions. They should avoid fresh peach as well as peach processed products. Certain patients with previous anaphylaxis or anaphylactic shocks should be trained in the early recognition and treatment of reactions in case of accidental ingestion, and given rescue medication including adrenaline.
Patients with peach allergy linked to birch pollen allergy should avoid fresh peach. Avoidance of peach processed products is generally unnecessary, but if their tolerance is unknown it should be assessed at the allergy clinic before allowing their ingestion.
If the tolerance to a related cross-reactive food (such as other Rosaceae fruits) is not known or has not been assessed after a confirmed diagnosis of peach allergy, patients should avoid it. This is especially important in patients sensitised to lipid transfer proteins who have had serious reactions with peach.