Sold under brand names like Prilosec (omeprazole) and Nexium (esomeprazole), PPIs treat reflux by curbing the production of stomach acid. With less acid in the digestive tract, however, people may also be become more sensitive to allergens from sources like food, pollen, or pets, says Erika Jensen-Jarolim, MD, the lead author of the study and an immunologist at the Medical University of Vienna in Austria. “Antacids like PPIs … lower the threshold for allergens to trigger allergic responses,” Dr. Jensen-Jarolim says. “Symptoms may occur at lower allergen exposure levels.” Stomach acid plays an important role in digestion, breaking down food and killing bacteria in the gut that can lead to illness or infections. Acid can also help act as a defense mechanism against microbes or proteins that might cause allergic reactions. It’s possible that depleting stomach acid might trigger allergies for the first time or exacerbate symptoms in people who already suffer from allergies, Jensen-Jarolim says. For the study, published in July 30, 2019, in the journal Nature Communications, researchers examined data from health insurance records covering 97 percent of the Austrian population between 2009 and 2013. Overall, people in the Austrian population who were prescribed acid-blocking drugs like PPIs were almost twice as likely to start new prescriptions for allergy drugs afterward than people in the population who never took PPIs. Women appeared to have a greater risk, and were more than twice as likely to take allergy drugs after starting pills like PPIs, compared with men. The risk also rose with age, climbing from 47 percent among people up to 20 years old on PPIs to a more than quintupled risk for people over 60. Researchers also looked at how often people took allergy medicine after being prescribed other common medicines, like pills to lower cholesterol or manage high blood pressure. People who took acid-blocking drugs were more than 3 times as likely to start using allergy medicines afterward than patients who took drugs for cholesterol or high blood pressure. Just six doses of acid-blocking drugs in a year were all it took for people to have a higher risk of using allergy drugs, the researchers reported. Higher doses of acid-blockers taken for longer periods of time were associated with a greater likelihood of allergy drug use. The study wasn’t a controlled experiment designed to prove whether or how PPIs or other acid-blocking drugs might directly cause allergies. One limitation of the analysis is that researchers lacked data on what diagnosis might have led patients to get prescriptions for PPIs or allergy drugs, or what specific allergy symptoms people had. Researchers also limited their analysis to antihistamines, which are prescribed almost exclusively for allergies, and didn’t look at other medicines, like corticosteroids, that are sometimes used for allergies but also prescribed for asthma and other conditions. Still, the results offer fresh evidence that patients should consider alternative to PPIs and other acid-blocking drugs when they can, and use these medicines for the briefest possible periods of time, Jensen-Jarolim says. There’s no way for patients to know if PPIs would trigger allergies in advance, says Saad Shakir, MBChB, director of the Drug Safety Research Unit in Southampton, England. “They will know when they get new allergic symptoms or worsening of preexisting allergic symptoms,” says Dr. Shakir, who wasn’t involved in the study. While using antihistamine prescriptions as a proxy for allergy flare-ups associated with PPIs, is reasonable, “it is not an actual allergy diagnosis,” Shakir says. The overall hypothesis of the study — that low acidity in the stomach makes it easier to for allergens to trigger allergic reactions — is also reasonable, Shakir adds. But even this large study “can only be considered as hypothesis strengthening, not a definitive study to answer the question” of whether PPIs cause allergies, Shakir says.
