The ‘allergic march’ shows how allergies can progress in kids

Eczema in young babies could be a sign that a child will go on to develop more allergies.

New research, published Tuesday in the journal Pediatrics, confirms a phenomenon known as the “allergic march” — a pattern that describes the way allergies tend to develop and progress in children, beginning in infancy through age 3.

The study, which analyzed medical records data collected between 1999 and 2020 from more than 200,000 children, found that kids tended to be first diagnosed with eczema, also called atopic dermatitis, at 4 months, on average. Next came diagnoses of food allergies that cause symptoms that range from hives to anaphylaxis — a life-threatening allergic reaction that affects the whole body and can cause the airways to swell and close — and asthma, both around 13 months old. At 26 months, the study found, children developed allergic rhinitis, or hay fever. In rare cases, children may go on to develop a fifth allergy, called eosinophilic esophagitis, by 35 months old.

Dr. Stanislaw Gabryszewski, a fellow in the Division of Allergy and Immunology at Children’s Hospital of Philadelphia who led the study, said the “allergic march” doesn’t mean every child who has eczema will develop every allergy described.

“Each child is different. Some may have one, others may have a couple, others may have all of them,” he said.

About 1 in 5 children has one of these types of allergies, making them one of the most common chronic illnesses in kids. Just over 13% of children have at least two types of allergic conditions, the researchers said.

The findings are helpful for both parents and physicians, who can monitor kids who develop eczema early in life more closely for other allergies later on.

“Eczema early in life is the No. 1 risk factor for developing allergies later in life, far more than family history,” said Dr. Ruchi Gupta, founding director of the Center for Food Allergy and Asthma Research at Northwestern University and Lurie Children’s Hospital of Chicago, who was not involved in the study.

The medical community has long recognized the allergic march, but the new research is the largest study to confirm the pattern. And while previous research primarily focused on white children, about one-third of the kids in this study were Black. About 10% were Hispanic and a smaller proportion — under 3% — were Asian or Pacific Islander.

“This study adds another layer of evidence that allergic diseases start early in life, and there is a progression of allergic disease that can occur together so that one child may have multiple allergic conditions,” said Dr. Sharon Chinthrajah, an immunologist at Stanford University School of Medicine who was not involved in the research.

She added that sometimes the earlier allergic conditions will go away, and the child will just be left with a food allergy, for example, but other times the allergies are cumulative, leaving children with multiple types of allergies. For some, certain allergies will come and go, Chinthrajah said. 

Food allergies were less common than previous research has found, affecting about 4% of the kids in the study, about half the amount seen in studies where people self-report their allergies. The most common food allergies were peanuts, eggs and shellfish. Patients with respiratory allergies like asthma and allergic rhinitis usually had both of those conditions, in addition to other allergic conditions.  

The study also found that eosinophilic esophagitis — a rare type of food allergy that causes inflammation in the esophagus — affects a larger proportion of nonwhite children than previously thought. About 40% of kids who had the condition were not white. Overall, this allergy was very rare, seen in just 0.1% of children. 

Better understanding how allergies commonly develop could lead to treatments that could halt the progression — or stop allergies from developing altogether.

If eczema could be prevented, “can we prevent food allergies, environmental allergies and can we prevent asthma?” Gupta asked. “We don’t know yet, but research is being done.”

Chinthrajah agreed. 

“Where it’s our job as researchers is to identify how do we intervene early and with those interventions, how do we influence not one of the five allergic diseases but many,” she said. 

That research will need to untangle the link between environmental factors — including climate change, which is making seasonal allergies worse — and genetics. 

“Ultimately it’s the interplay of the two that will dictate which children develop allergies and if they do, how severe they will be,” Gabryszewski said. 

Follow NBC HEALTH on Twitter & Facebook.