According to a paper published in the Journal of Pediatrics this month, the number of peanut allergy diagnoses among children has dropped over 40% since 2017.

The reason? Food allergy guidelines have undergone a massive sea change in the past decade.

In the late 1990s and early 2000s, parents were urged not to introduce their children to peanuts – one of the most common food allergens – until the child was at least three years old.

But in 2015, a blockbuster paper in the New England Journal of Medicine known as the Leap (Learning Early About Peanut allergy) study found that introducing the food to babies when they were just a few months old could reduce a child’s risk of developing the allergy by over 80%. Public health guidelines shifted and in 2017 the Prevention of Peanut Allergy Guidelines recommended introducing peanut protein to infants.

“A common misconception about food allergies is that delaying the introduction of allergenic foods may help prevent them,” says Dr Stanislaw Gabryszewski, an attending physician at the Children’s hospital of Philadelphia and one of the paper’s co-authors. “We now have strong evidence showing the opposite – that introducing peanuts and other common allergens early in infancy can actually reduce the risk of developing an anaphylactic food allergy.”

So how do allergies work? And how can parents cautiously introduce their children to food allergens like peanuts? We asked experts.

What are food allergies?

“When someone has a food allergy, their body makes antibodies called immunoglobulin E (IgE), directed against the food allergen,” explains Dr Hemant Sharma, the chief of allergy and immunology at Children’s National hospital.

Put another way: the body mistakenly identifies the food as something harmful and produces protective proteins (IgE), which bind to the food allergen and try to flush it out of the body. This results in symptoms such as hives; itchy skin; swelling of the face, lips or mouth; vomiting; diarrhea; difficulty swallowing and shortness of breath.

Food allergies are the result of “a complex combination of genetic and environmental factors”, says Gabryszewski. Allergies can run in families, but there can also be external influences, he explains.

The most common food allergies in children are milk, eggs and peanuts, Gabryszewski. “Most children tend to outgrow their milk and egg allergies, but peanut allergy tends to persist,” he says. In adults, some of the most common food allergies are peanuts, tree nuts and shellfish.

How common are peanut allergies?

Before the 1990s, peanut allergies were rare. While they are still not hugely common, numbers doubled in the late 1990s and early 2000s. According to one 2009 paper, the rate of peanut allergies among children in the UK rose from 0.5% to 1% between 1989 and 1994 to 1996, and US rates increased from 0.4% to 0.8% between 1997 and 2002.

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The increase was enough to prompt what some called a “peanut panic”. As peanuts and tree nuts account for the vast majority of deaths due to food allergies, many schools and airlines instituted peanut-free zones.

Recent studies have found that about 3% of US adults have a self-reported peanut allergy. And according to the charity group Anaphylaxis UK, about one in 50 children and one in 200 adults have a nut allergy.

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How can you cautiously introduce your child to peanuts?

Current guidelines from the American Academy of Pediatrics recommend parents introduce children to peanuts as early as four to six months of age. Children with eczema and egg allergies are at a higher risk of developing a peanut allergy and the guidelines suggest parents of higher-risk children may want to speak to a specialist first.

There are no exact guidelines about the amount and regularity of exposure. “An age-appropriate amount introduced ‘early and often’ is generally recommended,” says Sharma.

To prevent choking, experts say babies should be able to control their head and neck, and swallow food rather than let it dribble on to their chin before they try to eat any solid food. Even then, whole peanuts are a choking hazard for babies, and peanut butter can be difficult for them to swallow. Gabryszewski suggests thinning peanut butter in water or breast milk, “working towards about 2 tsp a few times a week”. McNairn also recommends Bamba peanut butter puffs, puffed peanut snacks that dissolve in the mouth.

While introducing any allergen to a child, McNairn says guardians should watch closely for signs of an allergic reaction, such as hives or vomiting. Mild symptoms including a rash or hives can usually be treated with an antihistamine, according to the Children’s hospital of Los Angeles. But if the child is vomiting, coughing or having difficulty breathing, seek medical attention immediately, either by getting a doctor on the phone or going to an emergency room.

If after several exposures to the food, the child has no negative reaction, they can probably tolerate it. It is also important to continue exposing them to the food, McNairn says. If a baby is exposed to a food and seems to tolerate it, but then that food is removed from the diet, “they could become sensitized to it,” she explains.

For this reason, McNairn recommends parents prioritize introducing their children to food that they regularly eat and have in the home. “If you’re eating communally at a dinner table, the baby’s going to want to eat what you’re eating,” she says.

Gabryszewski notes that early introduction does not necessarily prevent a food allergy. More research is needed on both prevention and treatment of these allergies, he says, but he is still optimistic about his recent study’s findings.

“This is a heartening indication that our growing emphasis on early introduction has been accompanied by a reduction in peanut allergy,” he says.