Food allergy occurs when a person’s immune system reacts inappropriately to proteins in a food. The first stage of the process is called sensitisation – when the immune system’s “memory” registers the food as a possible threat. Antibodies to that food are produced and, at a subsequent encounter, these antibodies may connect with the food’s proteins and trigger the release of certain substances in the body, such as histamine. This results in an allergic reaction. Some people, however, are sensitised to a food but never have an allergic reaction to it.
Pollen food syndrome usually occurs in people who are already allergic to pollens and suffer from hay fever, although the symptoms due to hay fever can be very mild. People with pollen food syndrome experience allergic symptoms when they eat certain fruits or vegetables. This is due to the similarities between the proteins found in pollen and those present in the fruits and vegetables. Symptoms are usually mild and may respond to antihistamines but it is important to consult your doctor to confirm that this is the right treatment.
Symptoms of pollen food syndrome usually include:
The proteins that cause pollen food syndrome are not very strong and are often changed by heating or acid in the stomach. It is thought that this is why people with pollen food syndrome are less likely to have a severe reaction than those with other food allergies. Most sufferers of pollen food syndrome experience allergy symptoms if they eat the raw fruit, but are able to eat the same food if cooked without any problem.
Some medical professionals refer to pollen food syndrome as oral allergy syndrome, although strictly speaking the two are not the same. When the term oral allergy syndrome was first used in 1987 it had no connection with pollen allergy but referred to any allergic symptoms in the mouth that often preceded more serious symptoms (AMLOT et al., 1987). Anaphylaxis UK prefers the term pollen food syndrome when referring to those allergy symptoms to food that are linked to pollen allergy, are limited to the mouth and throat, and are usually mild. Many people with fruit allergy are in this category.
Less commonly, people allergic to fruit have a different, more serious type of allergy. In some cases they may also be allergic to latex. Alternatively they may suffer from a newly recognised type of plant protein allergy called lipid-transfer protein (LTP) allergy. These conditions have the potential to cause more serious symptoms and there is a risk of anaphylaxis. Symptoms may include wheezing; a swelling of the throat that is serious enough to restrict breathing; and even a fall in blood pressure that can lead to collapse. Accompanying symptoms may include widespread flushing of the skin, nettle rash (otherwise known as hives or urticaria), swelling of the skin (known as angioedema) anywhere on the body, swelling of the lips, or abdominal pain, nausea and vomiting.
If you are at risk of anaphylaxis, self-injectable adrenaline (EpiPen, Jext or Emerade) will be prescribed as well as an antihistamine.
Click here to read our factsheets about anaphylaxis and adrenaline.
Read more about Lipid Transfer Protein Allergy.
Soya – a particular concern for some people
The medical expert who reviewed this article tells us that many people with pollen food syndrome who react to fruit also react to raw soya (such as soya drink, soya yoghurt, raw tofu). For some reason, the first sip of a soya drink (or first spoonful of soya yoghurt) does not alert them sufficiently and they may consume the whole portion. Reactions can then be severe due to the quantity consumed and on rare occasions anaphylaxis can be the outcome. This does not affect everyone with pollen food syndrome, but we advise that if you suffer from pollen food syndrome be cautious when consuming large quantities of soya (such as soya drink). A severe reaction is highly unlikely but if there is wheezing, difficulty breathing or a feeling of faintness or dizziness, administer adrenaline (if available), then dial 999 and say the person is suffering from anaphylaxis (anna-fill-axis).
Some people who experience symptoms when they eat a food do not have a true allergy, but rather a food intolerance. Whereas food allergy is a reaction of the immune system, food intolerance may have a different cause. A much wider range of symptoms can occur. There may be migraine and unexplained fatigue, abdominal pain, bloating and frequent diarrhoea, unexplained muscle and joint pains or unexplained nasal congestion and discharge. Food intolerance to fruits could be part of a wider intolerance to foods because of a sensitivity to naturally occurring ‘food chemicals’ in the fruit, or due to an inability to properly digest fructose, the natural sugar found in many fruits.
Allergy to vegetables
The key message
Medical advice is required in all cases where fruit causes symptoms. This will determine what type of allergy you have. Is it pollen food syndrome or is it in the more serious category? Or do your symptoms have a non-allergic cause such as food intolerance?
Recently our medical advisers have made us aware of an increasing number of allergic reactions to jackfruit, which is becoming popular among people following a vegan diet.
If you are allergic to one of more of the above fruits, this does not necessarily mean you will react to any others in the list. However with some fruits there is a possibility that you will. Medical advice is needed in all cases of allergy to fruit.
If you suspect you have a food allergy, it is important to see your GP as soon as possible. Some GPs have a clear understanding of allergy, but allergy is a specialist subject your doctor may need to refer you to an allergy clinic. Anyone who has suffered anaphylaxis should certainly be referred.
Your GP can locate an allergy clinic in your area by visiting the website of the British Society for Allergy and Clinical Immunology
Once you get a referral, the consultant will discuss your symptoms with you in detail as well as your medical history. Skin prick tests and blood tests may help form an accurate picture. When doubt remains, the consultant may suggest a “food challenge”– where the patient eats a small amount of the suspect food, increasing the dose gradually, to test whether or not a reaction occurs. This must only be done by an experienced consultant in a medical setting.
If symptoms triggered by fruit occur only in the mouth, the likelihood is that your allergy will remain mild but medical advice on this must be sought.
The presence of asthma – especially when poorly-controlled – is known to be a major risk factor for the occurrence of more severe allergic reactions. We recommend that everyone with asthma should be seen at least once each year by their GP or asthma nurse to ensure their symptoms are well managed.