What do peanuts, shrimp, and eggs, have in common?—On the surface, nothing much. But all of the above, it turns out, are common causes of food allergies. About 15 million Americans are allergic to food, with miserable symptoms that range from hives and rashes to runny noses, dripping eyes, coughing, sneezing, shortness of breath, and even the very worst case scenario—anaphylaxis and death.
About 90 percent of these allergies are reactions to just eight foods. The chief culprits are milk, eggs, peanuts, tree nuts, soy, wheat, fish, and shellfish. One out of every 13 kids has a food allergy—an average of two per classroom nationwide. Many grow out of their milk, egg, and soy allergies, which are often history by the time they’re teenagers, but the three million who are allergic to peanuts and tree nuts are generally stuck with the condition for life.
Allergies are the result of a normal human system run amok. All are hyperimmune responses, in which the body’s immune system—which functions to protect us from disease— suddenly begins to respond, often dramatically, to substances that it ordinarily should ignore. The body’s adverse reaction to an allergen begins with the release of an antibody known as immunoglobulin E (IgE), which in turn triggers the release of histamine, a tiny molecule with a large range of effects. At the annoying end of the scale, these include itching, redness, and swelling. At the dangerous end, blood vessel dilation can lead to a precipitous drop in blood pressure, difficulty in breathing, and anaphylactic shock. The severely allergic defend against this by carrying injectable epinephrine.
We know how allergic reactions work and we know their proximate causes, but why do allergies develop in the first place? And why are they on the rise?
Figures vary, but scientists agree that the trend for allergies in developed countries is steadily up. One often-cited study from the Centers for Disease Control and Prevention (CDC), for example, showed an 18 percent increase in food allergies in children between 1997 and 2007; another, released in 2013, cited a 50 percent increase as of 2011.
“Developed countries” may be the key term here. Though most scientists agree that allergies are likely the result of complex interactions between genes and the environment, a common explanation for the current storm of sensitivities is the hygiene hypothesis, which argues that in many places, life has become too clean. A combination of sanitation, modern medicine with its battery of bug-killing antibiotics, and an increasingly dirt-free indoor lifestyle has caused us to lose a lot of beneficial microbes that evolutionarily have beefed up our immune systems and ensured the health of the epithelium of the digestive tract. When the epithelium gets weak and leaky, bacteria and bacterial byproducts can escape their natural home in the gut and enter the bloodstream, leading to inflammation and contributing to a host of chronic diseases, among them allergies and asthma. (See What’s Up With the Bacteria in Your Gut?)
A related factor in the rise of allergies may be the increasing incidence of birth by Caesarean section. An estimated 4.5 percent of babies were born by C-section in 1965; today it’s over 30 percent. C-section babies are up to five times more likely to develop allergies than those delivered naturally—possibly because C-section kids miss out on the helpful gut bacteria ordinarily acquired during unsterile passage through the birth canal.
Then there’s the question of genes. Studies with identical twins who share the same complement of genes and fraternal twins who don’t indicate that heredity plays a sizeable role in allergies. One report showed that about 65 percent of identical twins shared peanut allergies, as opposed to just 7 percent of fraternal twins. Just which gene or genes contribute to allergies remains a mystery, though some evidence points to mutations in the gene BACH2 – named for the composer – that appears to play a role in allergies and autoimmune diseases such as Crohn’s disease and Type I diabetes. Another possible contributor is the gene that codes for a growth factor called TGF-beta, mutations in which lead to the chain reaction of events that results in allergies.
Gene-wise, there’s also a chance that our modern plague of allergies may be at least partially the fault of the Neanderthals. Today, the DNA of all non-Africans contains 1 to 6 percent Neanderthal genes, the legacy of hot interspecies sex that took place some 40,000 years ago. Three distinctive genes are among our most common Neanderthal leftovers and all have to do with the immune system. We’ve held on to these for so long because they confer an evolutionary advantage, helping to protect us from pathogens. But scientists believe that they just may do their job too well, leading to hyperactive immune responses and predisposing their carriers to allergies.
Despite some public allegations, there’s no scientific evidence that vaccines cause allergies, though physicians caution that children with existing food allergies may have adverse reactions to food-related compounds such as egg proteins in certain childhood vaccines. Similarly, despite consumer concerns, GMO foods are off the hook, allergy-wise. Scientists point out that GMO foods, which are heavily tested, actually have less allergenic potential than new conventional foods, which may contain hundreds of new food proteins. Genetic modification may even eventually provide help for allergy sufferers. Work is underway, for example, to develop a safer hypoallergenic peanut.
Clearly, when it comes to allergies, there’s more research to be done. In the meantime, the best approach for those with allergies is caution.