Banana is the crescent-shaped edible fruit of any of several species of the musaceous genus Musa, which are tropical and subtropical herbaceous tree-like plants. Meanwhile, Plantain specifically refers to the fruit of Musa paradisiaca, a large tropical musaceous plant, eaten as a staple food in many tropical regions. World banana production is about 65 million tonnes per year, concentrated in Africa, Asia, the Caribbean and Latin America, due to climatic conditions. In Europe, estimated yearly consumption varies among countries, from 5 to 10 kg/capita in the Mediterranean area and the Netherlands, to more than 15 kg/capita in Sweden.
Banana is mainly consumed as a fresh fruit, although a growing variety of processed foods may contain it. These include juices, syrups, spirits, fruit shakes, fruit cocktails, mixed dried fruits, ice creams, yogurts and other dairy products, puddings, breakfast flakes, energy bars, flavouring powders or essences, confectionery, baked goods, and fruit sauces. Moreover, some drugs may also contain banana, as a flavouring additive, as well as some cosmetics.
Symptoms
Patients with allergy to banana report adverse reactions immediately after banana consumption, i.e., up to 1 hour after ingestion of either fresh banana or of a banana-containing food. Symptoms are characteristics of food allergy: from mild reactions, such as itching and mild swelling of the lips, tongue, palate and throat, followed by a rapid resolution of symptoms, to itching rush and hives in the skin or mucous swelling, stomach complains, hayfever, constriction of the throat and asthma, or anaphylactic shock – a generalized life-threatening reaction with a large drop in blood pressure.
How much is too much?
There is a lack of information on lowest threshold dosages able to induce such reactions but, in a study including food challenges, one patient reacted 5 minutes after a dose of 1.3 g of banana. Anyway, data obtained from clinical histories suggest that, in highly sensitive patients, a very small piece of banana could be enough to trigger reactions.
Related foods (cross reactivity)
Banana allergy rarely presents as an isolated disorder, due to cross-reactivity with allergens from other sources. In fact, accompanying allergies to other plant-derived foods are almost the rule. Moreover, most banana allergic patients show associated allergy (hayfever or asthma) to pollens, and/or allergy to natural rubber latex. However, proportions of other food-, pollen-, or latex-associated allergies may greatly vary among different populations, as a function of selection criteria, as well as of pollen or latex exposure.
Latex is the milky sap of Hevea brasiliensis tree, which is processed to manufacture multiple products, including gloves, condoms and balloons. Latex allergy has been recognized as a very important health problem, due to increase in frequency, and to its ability to induce severe reactions. It is noteworthy that as much as 50% of latex allergic patients may have cross-allergic reactions to certain plant-derived foods (mainly banana, chestnut, avocado and kiwi), a condition known as the latex-fruit syndrome. Allergens responsible for this syndrome seem to be a group of shared plant proteins, to which patients react.
Interestingly, the content of these allergic proteins in fruits can be increased by certain chemical or physical factors. For example, some chemical products used for ripening bananas, clearly induce allergens, therefore rising fruit allergenicity. These proteins seem to be inactivated by heating, which could explain why some plant foods containing these allergens, but only consumed after cooking, are not associated with this syndrome.
With respect to banana-pollen allergy, several patterns of associated allergies have been described. Examples for that are the following clusters: ragweed pollen allergy with banana and melon allergies; multiple pollen allergies with banana, melon, watermelon, citrus fruits and tomato allergies; and Platanus tree pollen allergy with banana, hazelnut, peanut and celery allergies. A group of allergens very common in the plant kingdom seem to be responsible for at least part of these cross-reactions, but other allergens may also be involved.
Who, when, how long, and how often?
Unfortunately, there is scarce data on the occurrence of banana allergy in different age groups and geographical areas. It seems that, although it is not among the top-5 food allergies, it cannot be considered as a rare allergy, neither in children nor in adults. Certainly, it is much more frequent among specific groups of patients, as for example subjects allergic to latex, to pollens, or to plant-derived foods. In the same way, the development of banana allergy is not known, as long-term follow up of banana allergic patients have not been conducted. Nevertheless, clinical data suggests that patients allergic to banana should assume a lifelong avoidance diet, since – to our knowledge - patients outgrowing banana allergy have not been reported.
Diagnosis
With no doubt, clinical history is the best way to detect banana allergy. Patients with immediate reactions after banana ingestion, suggestive of a food allergy (see symptoms), should look for medical advice, and avoid banana consumption until diagnose is established. There are banana extracts commercially available for performing skin tests, as well as assays for blood samples. However, both types of tests currently used do not detect all banana allergic patients. To try to improve diagnostic sensitivity, a prick-prick with banana – skin test with the fresh fruit - can be performed.
At the same time, neither skin tests nor specific IgE to banana are 100% specific, which means that a positive test only demonstrates reaction of the immune system but not predicts allergy. Therefore, data must be always interpreted according to clinical history. Frequently, and if a not-severe reaction is expected, a controlled oral challenge test (ingestion of progressive doses under close medical supervision) is the only way to discern whether a given patient is truly allergic to banana, but this may present risks in some patients.
Avoidance
Patients suspected of being allergic to banana, should completely avoid the ingestion of both fresh bananas and of any banana-containing food, until evaluated. Once diagnose of true banana IgE-mediated allergy is confirmed, patient should follow a lifelong banana-free diet. They should also take care of possible unadvertised exposures, since – unfortunately - this food has not been included in the list of potential allergenic ingredients to be labelled, of the new EU labelling directive (2003/89/EC).
Due to cross-reactivity, patients considered to be at high risk of banana allergy, as for example subjects allergic to latex, avocado, chestnut, kiwi, melon, or to certain pollens, should be carefully asked about possible previous adverse reactions on banana ingestion. Unless consumption of banana with perfect tolerance is reported by the patient, a banana-free diet should be recommended, until proper diagnosis - on the basis of objective procedures to evaluate clinical reactivity - is made.
