'Adult-Onset Food Allergies Warrant ‘High Index of Suspicion’'

 Anecdotal and survey evidence suggests that adult-onset food allergies may be increasing.

“We don’t talk about it enough, but adult food allergy is real,” Ruchi Gupta, MD, MPH, told Medscape Medical News.

In 2019, Gupta, director of the Center for Food Allergy and Allergy at the Institute for Public Health and Medicine at Northwestern University in Chicago, and her colleagues published results from a survey of over 40,000 US adults that found more than 10% reported an adult-onset food allergy. Among these food-allergic adults, 51.1% reported having had a severe food allergy reaction. The study results were published in JAMA Network Open.

An independent analysis of private health insurance claims from 2007 to 2016 supports Gupta’s group’s finding. The nonprofit, FAIR Health, found that claims submitted during that period for food allergy-related anaphylaxis treatment increased by 377%. Of these claims, more than a third (34%) were made by adults aged 18 years or older.

Gupta said allergic reactions are the same in adults as in children: pruritus, urticaria, gastrointestinal distress, anaphylaxis, and possibly even death. In the survey by Gupta and coworkers, more than a third of respondents with food allergies (38.3%) had received emergency department care due to a food allergy at least once in their life.

Most Common Adult-Onset Food Allergies

“The foods that adults might be allergic to are not quite the same as kids, so maybe that’s some of what is going on here. With kids we think of peanut, milk, and egg,” said Edwin Kim, MD, MS, the Division Chief of Pediatric Allergy and Immunology at the University of North Carolina (UNC) at Chapel Hill, and director of the UNC Food Allergy Initiative.

The most common food allergy that adults seem to develop is shellfish, Gupta said in an interview. “They hate it because they love shellfish and say they ate it all their life. Now they get hives when they eat it,” Gupta said.

Then there is the meat-based alpha-gal allergy that Kim said is a growing concern, especially in the Southern US. Alpha-gal is the oligosaccharide galactose-alpha-1,3-galactose, a sugar found in most mammals, but not in humans or other primates. It also is found in tick spit, specifically the lone star tick (Amblyomma americanum). Persons who’ve been bitten by the lone star tick are at risk for alpha-gal syndrome, which makes them allergic to this sugar found in meat.

It’s tough to tell a meat-eating adult that a tick bite means they can’t eat meat anymore, Kim said.

Causes of Adult-Onset Food Allergies

Globally, food allergies are on the rise across pediatric and adult populations, although estimates vary, according to a 2012 review in Clinical and Translational Allergy. A more recent review in Frontiers in Nutrition in 2024 suggested that the increase is more prevalent in wealthy nations.

The etiology remains a mystery, however.

The genetics from one generation to the next doesn’t change that much, Gupta said. “So…what is in the environment?” Is it related to the microbiome and how our diets have changed?

“If it is an environmental factor, we are seeing something happen that triggers a switch in adults,” Gupta said. “Then they start reacting to these foods the same way a child would.”

Gupta said some of the environmental pathways she and her colleagues are studying involve whether a novel food allergy might be related to a life change. This might include moving or having a viral or bacterial infection that might have delivered a blow to the immune system.

Whether adult-onset food allergies are related to hormonal changes is also on the table, according to Gupta. “We do hear women saying that they developed a new food allergy during the time of pregnancy or menopause,” she said.

As for the growing prevalence of shellfish allergy, Jay Lieberman, MD, a professor of pediatrics at The University of Tennessee Health Science Center in Memphis, Tennessee, told Medscape Medical News that it is likely due to airborne exposure to dust mites and cockroaches; the allergen is the same and cross-reacts with shrimp allergen.

“You develop the dust mite and cockroach allergy first,” he said, “and can later develop symptoms to shrimp.”

In a review published in Annals of Allergy, Asthma, & Immunology of adult-onset allergies, Lieberman and his co-author warned clinicians to have a “high index of suspicion” for shellfish allergy in adults.

Undiagnosed vs Diagnosed

The results of the survey by Gupta and colleagues also found many adults who do not have an actual food allergy believe that they do.

About 1 in 5 of the survey respondents were convinced they had a food allergy, but only about half reported their allergy had been diagnosed by a physician (47.5%). Individuals with peanut allergies reported the highest rate of physician diagnosis (72.5%).

So, about 20% of adults avoid a food because they think they are allergic to it, Gupta said.

About 8% of children in the US have a diagnosed food allergy, according to the CDC, and now, the survey by Gupta and colleagues shows about 5% of adults have one. “So, the numbers are comparable,” Gupta said.

Gupta theorized that people often mistake a food intolerance for a food allergy. Some people may mistake food poisoning for a food allergy. Most likely, these people will not have their suspicions validated by an allergist.

“It is crucial that adults with suspected food allergy receive appropriate confirmatory testing and counseling to ensure a food is not unnecessarily avoided and quality of life is not unduly impaired,” she said.

Gupta disclosed receiving grant or research support from Genentech, The Melchiorre Family Charitable Foundation, Sunshine Charitable Foundation, the Walder Foundation, Thermo Fisher Scientific, and UnitedHealth Group, and membership on an advisory committee or review panel for Genentech. Lieberman and Kim reported having no relevant disclosures.

https://www.medscape.com/viewarticle/adult-onset-food-allergies-warrant-high-index-suspicion-2025a1000rdd