Food allergy affects up to 6% of young children and 3.5% of adults in the United States. In contrast to 30 or 40 years ago, it is not uncommon to know a family member, neighbor, or friend affected by a food allergy. There has been a growing concern that this phenomenon represents an increase in the prevalence of food allergies rather than a greater public awareness or better media coverage of the problem.
Based on large-scale population studies, there is good evidence that allergic diseases such as allergic rhinitis (hay fever), asthma, and atopic dermatitis (eczema) have increased in the last few decades.
Evidence is now mounting that there is a rise in the occurrence of food allergies that appears to parallel the rise in other allergic diseases. Direct evidence for the increase in food allergies comes from two studies that focus specifically on peanut allergy.
In one study, Jane Grundy of The David Hide Asthma and Allergy Research Centre and her colleagues looked at groups of children aged three to four, born at two different time periods on the Isle of Wight in England. There were over 1,000 participants in each group. Parents of these children completed questionnaires about symptoms of allergic diseases, including food allergy. Children also had allergy skin tests performed.
Those with positive skin tests to peanuts who had not had a convincing allergic reaction to peanut, or who had never eaten peanut, were offered food challenges to confirm peanut allergy.
The investigators found that the number of children with reported peanut allergy (by questionnaire) had doubled from 0.5% to 1% over the five-year time period. The proportion of children with positive skin tests to peanut had increased threefold from 1.1% to 3.3%. In children with positive skin tests, the overall estimate of true peanut allergy was 1.5% when adding up those with convincing clinical reactions and positive food challenges.
In the United States, Dr. Scott Sicherer and colleagues, using a nationwide telephone survey with over 10,000 participants, found that the rate of peanut allergy doubled in children from 0.6% to 1.2% over a five-year period.
What is surprising is that only three-quarters of the children and less than half of the adults in this study sought a medical evaluation of the allergy despite reporting severe reactions and multiple reactions during their lifetime.
Of those who did seek medical evaluation, fewer than half received a prescription for self-injectable epinephrine. We still are awaiting studies to be performed regarding the possible increase in prevalence of other common food allergens.
Why are food allergies on the rise?
Several theories have been put forth to attempt to explain the rise in food allergies. One leading theory is the “Hygiene Hypothesis,” first proposed by British researcher Dr. David Strachan in 1989.
This theory states that exposure to certain germs and infections early in life are important in training the immune system to do what it is intended to do— recognize foreign threats to the body. The Western lifestyle of cleanliness and obsession with hygiene has skewed the immune system toward the development of allergic diseases.
Studies done in Europe found that children raised on farms and rural areas, where there was exposure to bacteria from animals, had fewer allergic diseases compared with those living in cities.
Similarly, children who attend childcare or who have older siblings, thus having greater exposure to infections, have a decreased incidence of asthma and wheezing.
Another explanation for the rise in food allergy is introduction of foods too early in an infant’s diet, before the immune system is mature enough to handle them. This could occur through breastfeeding or an unintended exposure to highly processed foods in the Western diet that may contain hidden sources of the allergens.
Cooking practices can also affect the development of food allergies. For example, roasting a peanut enhances its allergenic potential compared to other forms of preparing peanut. Peanut allergy is more common in the U.S. where peanuts are roasted, as compared to China where peanuts are boiled.
What is on the horizon for management and prevention of food allergies?
New treatments of food allergy are emerging. These include procedures for desensitization that change the way the immune system responds to allergens, much in the same way allergy shots work for hayfever.
There are ongoing studies to attempt allergy desensitization by the injection of peanut protein that has been modified to prevent an allergic reaction but is still recognized by the immune system as the food protein. Studies are also ongoing to attempt desensitization by the oral route, where different immune mechanisms are likely at play.
The question remains whether we can combat the rise in food allergies by preventing the occurrence of food allergies in the first place. These include studies with maternal avoidance of common allergy-causing foods during pregnancy and while breastfeeding, and delaying introduction of solid food in an infant’s diet. Unfortunately, many of these studies have yielded conflicting results that do not allow us to make definite recommendations other than delaying introduction of solid foods until six months of age.
Nevertheless, the rise in food allergies has created an urgency to understand what makes some foods allergenic and to identify the risk factors of developing food allergies in order to define better strategies for prevention.
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