Over 4.6 million US adults have a peanut allergy – and many of them developed the allergy in adulthood, a new study has found.; A peanut allergy has generally been thought of as a pediatric issue, but more adults than children have the allergy, said study author Dr. Ruchi Gupta, director of the Center for Food Allergy and Asthma Research at Northwestern University in Illinois. But only 15% to 20% of children with a peanut allergy will outgrow their allergy by adulthood, according to the study.