Are Allergies Hereditary? The Science Of Allergies, Explained

Introducing your kid to new foods should be a fun experience, but there’s a hidden danger that can make taste-testing a disaster: anaphylaxis, or a severe allergic reaction. Many allergies are mild and only result in occasional sniffles, but others can be fatal. With allergies becoming more common over the past 50 years and today affecting upwards of 40% of the population worldwide, parents may wonder where allergies come from and if they’re responsible for passing down allergies to their children, or if there’s a way to prevent their kids from developing allergies. In other words, are allergies hereditary?

Children can inherit the tendency to be allergic — a characteristic known as atopy — from their parents, according to Richard Wasserman, M.D., Ph.D., medical director of Pediatric Allergy and Immunology at the Medical City Children's Hospital in Dallas, Texas. Just as each child’s hair color is uniquely positioned on a spectrum from flaxen blond to coal black and determined by the complex interactions of more than 120 genes, so too do allergies develop when a host of different gene patterns combine in children.

Children with allergic parents have between a 50% to 80% chance of developing allergies. And maternal allergies are more likely than paternal allergies to lead to the child inheriting allergies. However, it’s not like a mother’s allergies to penicillin will be directly inherited by her child, Wasserman says. “Although we know significantly more about the genetics of allergy today than we did even 10 years ago, it is enormously complex and we still only have a limited understanding,” he says.

There are often many genes at play that can be triggered by various allergens in the child’s environment, he explains. For example, people may inherit the tendency to be allergic from their parents, but then develop pollen allergies specifically to the regional pollen in their environment.

“People inherit the ability to be allergic, but they don’t inherit what they’re allergic to,” Wasserman says. “In the same family, there can be people who are allergic to cats and other people who are allergic to peanuts and other people who have hives, and some people who have more than one of those problems.”

The effects of the environment on developing allergies is often mediated by epigenetic modifications, which are changes to DNA, but not to genes themselves. Epigenetic modifications do, however, change how how the body reads those genes. Epigenetic changes are known to play a role in hay fever, food allergies, asthma, eczema, and other allergy disorders.

Sparse studies have linked individual genes with specific allergens. For example, gene variants in the human lupicize antigen (HLA) complex — the same region that can help determine genetic compatibility of transplants — have been linked to peanut allergies. A recent study linked mutations on the filaggrin gene — related to the skin’s barrier and moisturization — to milk and egg allergies. And scientists have long thought asthma is associated with several different genes related to the immune system.

Allergens are also connected to one another through a process called the “allergic march,” in which many children first develop eczema, followed by food allergy, and then asthma and nasal allergies. All of this occurs within the first six years of life.

The allergic march is thought to occur as a result of certain gene mutations and environmental factors, but it’s unclear why some children will outgrow certain allergies and others continue along the march. Luckily, it is possible for parents to disrupt the allergic march by treating problems like eczema as they come up, Wasserman says.

There are no foolproof ways to prevent a child from developing allergies, but there are ways to lower the odds. Exposing children to certain allergens in specific ways has been shown to reduce their risk of developing an allergy to that substance later on.

For example, some studies show pet dogs decrease the risk of asthma when introduced in the first year of life, and that children who grow up in rural farmlands with lots of animals have a lower risk of developing allergies than children who grow up in urban cities. But owning a cat has been shown to increase the risk of cat allergy in countries without many of these animals and decrease it in countries like the U.S. that have a lot of cats, so introducing the allergen early may not always be helpful. It’s not a straightforward relationship.

Similarly, when it comes to food allergies, the American Academy of Pediatrics currently recommends introducing so-called “problem foods” — such as milk, eggs, and peanut butter — around four months, once a child is accustomed to eating solid foods, to reduce the risk of developing an allergy to them.

However, kids who are exposed topically, or through the skin, to foods like peanuts have been shown to have a higher risk of developing allergies. Food sensitization is especially likely to develop when children are exposed through skin damaged by eczema, Wasserman says. That’s why treating eczema and maintaining good skin care is so important, he adds.

A child’s pediatrician may recommend oral immunotherapy, a process in which doctors feed allergic children portions of food allergens to build up a tolerance. Once children are a bit older, doctors may also recommend using allergy shots to treat them, Wasserman says.

One theory regarding why allergies are becoming more prevalent these days, called the “hygiene hypothesis,” stems from the idea that exposure to microbes and germs decreases the risk of allergies. The idea is that while sanitizing can be helpful in preventing the spread of harmful germs that spread infections like COVID-19, over-hygienic environments also remove non-harmful germs that build up the immune system.

“If there is exposure to germs that are not disease-causing, that’s how the immune system develops,” Wasserman says. “Being in an environment devoid of germs increases a lot of problems, but it probably also increases allergy.”