Study shows adults can develop food allergies - Winfield Hospital - 24 August 2017

Study shows adults can develop food allergies
Thursday 24 August 2017

It's often thought that if you have a food allergy, you'll have it from childhood. But an American study has found that over half of people with food allergies develop them after the age of 18. What kind of allergies do adults get and is there a difference between them and childhood allergies?

Increase in food allergies

Food allergies in children are becoming more common and more severe. Research a few years ago revealed that almost 8% of children in the US had a food allergy; with 40% of those children having a severe allergy. Two-thirds of children were found to have sensitivity to more than one type of food.

But what about adults? Can food allergies start in adulthood? According to a new US study, yes. It found that nearly 52% of Americans with food allergies develop them after the age of 18.

In addition, although children may grow out of their allergies (particularly allergies to milk, eggs or wheat), once an adult develops one, it usually remains with them for the rest of their life.

Shellfish the most common allergy

This new study estimated that 5% of adults in the US have a food allergy. This is based on a national survey conducted with over 40,000 adults.

The most common food allergy in adults according to the study is shellfish (affecting 3.9% of Americans), followed by peanut allergy (2.4%) and tree nut allergies, including walnut, almond, cashew and brazil nuts (1.9%).

Although the top eight foods that people are allergic to (milk, eggs, wheat, soy, peanuts, tree nuts, fish and shellfish) are generally the same in children and adults, there are differences in how they are experienced. For example, shellfish allergy is more common among adults than among children, as it tends to appear later in life.

Peanut allergy

Peanut allergies typically develop during childhood, and children are less likely to outgrow them than they are other food allergies. Peanut allergy appears to be equally prevalent among adults and children.

A lot of research has been done into peanut allergy, particularly into finding a cure or treatment, as it can be so serious.

Recently a treatment for peanut allergy was found to be effective for four years. An Australian research team gave a probiotic to children every day for 18 months. After four years, 70% of the children were able to eat peanuts without any allergic reaction.

Oral allergy syndrome

Adults are more likely than children to get ‘oral allergy syndrome’ - where people with an allergy to tree pollen also develop an allergy to some raw fruit and vegetables. The syndrome is caused by the immune system confusing proteins in tree pollen to those in uncooked fruit and vegetables.

People who have this syndrome may get a tingling or itching in the mouth and throat. It usually goes as soon as the person stops eating that particular food.

Causes of allergies

Food allergies happen when the immune system mistakenly treats proteins in food as a threat and releases chemicals. These chemicals cause the symptoms of an allergic reaction.

It is not known exactly why adults develop food allergies, but there are many theories, including globalisation of the food we eat, environmental factors, changes to our immune system and hormonal changes in adulthood, for example pregnancy. Some people find they develop a new allergy after having had a viral infection, although it is not known why this might happen.

Food intolerance

Having a food allergy is different to having a food intolerance, although the two are often mixed up.

People with food intolerance may have symptoms such as diarrhoea, bloating and stomach cramps, which occur several hours after eating the food. An allergic reaction will occur much sooner after having the food and will usually result in symptoms such as itching, a rash, swelling, trouble breathing or vomiting.

The immune system is not involved in a food intolerance. There is no allergic reaction and it is never life-threatening. It also only develops if you eat a reasonable amount of the food, whereas with a food allergy, mere traces of that food can trigger the allergic reaction.


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