Developing or losing allergies in adulthood isn't unusual, but why certain allergies come and go is largely not understood by scientists, Hannah Seo reports for the  New York Times.

What experts know about allergies

Allergies can develop and change over time, especially in adulthood. According to  CDC, around 26% of adults and 19% of children in the United States have a seasonal allergy, while around 6% of adults and children have a food allergy. These allergies occur when the immune system mistakenly reacts to allergens, such as pollen or animal dander, causing a range of symptoms from sneezing to anaphylaxis. 

Experts believe factors such as puberty, pregnancy, illnesses, and organ transplants may play a role in these allergic responses. In a 2018  survey  of over 40,000 US adults, Ruchi Gupta, a professor of pediatrics who specializes in allergy at the  Northwestern University Feinberg School of Medicine, and colleagues found that 45% of those with food allergies developed at least one new food allergy in adulthood, with a quarter of them never experiencing food allergies in childhood.

Why some allergies develop or disappear

According to Jyothi Tirumalasetty, a practicing allergist and clinical assistant professor of medicine at  Stanford University, "losing" an allergy or becoming "desensitized" to an allergen is quite common, especially after middle age, as immune responses naturally lessen with age. Certain allergies, like penicillin and seasonal allergies, are more likely to resolve over time.

While it's rarer for adults to outgrow food allergies like tree nuts, fish, and shellfish, it's estimated that 50% to 80% of children with milk or egg allergies grow out of them by age 10.

In some cases, people may develop allergies in adulthood they've never had before. For example, people who move to a new area may encounter pollen they've never been exposed to before, said Shradra Agarwal, an allergist and immunologist at the  Icahn School of Medicine at Mount Sinai. And while this isn't technically a "new" allergy, that distinction can make the area difficult to research.

Can adulthood allergies be prevented?

Unfortunately, there isn't a clear answer for how adults can prevent new allergies from developing, Agarwal said. According to Gupta, most allergy prevention research is currently focused on preventing food allergies in young children.

Corinne Keet, a professor of pediatric allergy immunology at the University of North Carolina School of Medicine, emphasizes that there are no ways to control or predict the development of new adult allergies. As a result, she said, "I wouldn't worry about it." (Seo, New York Times, 4/19)