Now, a new study shows just how widespread peanut allergies are among adults in the U.S. A study published Tuesday shows that there are more than 4.5 million adults who are allergic to peanuts. Of them, nearly a million developed the allergy once they reached adulthood.; Dr. Ruchi Gupta authored the study along with Dr. Christopher Warren as part of their work at the Center for Food Allergy and Asthma Research at Northwestern University. They say peanut allergies are generally thought to be a condition in children, but their research finds more adults than children have the allergy. They say they hope their study prompts more adults who suspect they have an allergy to get a confirmation.