A new study shows that allergies to foods can start in grownups, and unlike childhood allergies, they usually persist

You have always loved prawns, but suddenly they make your mouth tingle. You bite into an apple and your throat feels itchy and tight. But surely they can’t be food allergies if you have eaten them all your life without problems? Should you ignore the symptoms, or cross prawn cocktails and apples off the menu?

The solution

Allergies can indeed start in adulthood. Nearly 52% of Americans with food allergies develop them after the age of 18. This preliminary data comes from a national study that shows shellfish is the most common food allergy in adults (affecting 3.9% of Americans), followed by peanut allergy (2.4%) and tree nut allergies, including walnut, almond, cashew and brazil nuts (1.9%).

Whereas children may grow out of allergies, especially those to egg, milk and wheat, once an adult develops a food allergy, it usually persists, says Dr Stephen Till, consultant allergist at Guy’s and St Thomas’ NHS foundation trust.

Adults are more likely than children to get oral allergy syndrome – a type of food allergy caused by raw apples, fruits with stones and uncooked vegetables. The most common symptom is tingling in the mouth and throat that starts as soon as you begin eating and goes very quickly. It affects people who are allergic, even mildly, to birch tree pollen or grass pollen.

The syndrome is caused by the body’s immune system confusing proteins in pollen with those in raw fruit and vegetables. Stomach acid destroys the proteins quickly, so the effects usually go as soon as you swallow. If you have the syndrome, you should avoid smoothies as concentrated doses of raw fruit or veg can provoke more serious symptoms such as a rash, tight chest and wheezing.

We don’t know exactly why adults suddenly become allergic to foods, says Till. One theory is the globalisation of the food industry. As he points out, the prawns we got used to in our cocktails are a different species from the Vietnamese tiger prawns available today.

There is not an inevitable rise in the severity of reactions. Till says lots of factors influence an allergic reaction, including how much of the allergen you eat, and how much alcohol, exercise, stress and sleep deprivation you have had. Genetics also plays a part. However, if you have any symptoms of any severity, you should see your GP – and ideally a specialist.

A guide by Sense About Science warns of some of the mythology about allergies: for example, far more people think they have a food allergy than actually do.