In the past 30 years, food allergies have become increasingly common in the United States. Changes to human genetics can't explain the sudden rise. That is because it takes many generations for changes to spread that widely within a population. Perhaps the explanation lies in changes to our environment, particularly our internal environment. Shifting lifestyle practices over the last half-century—increasing antibiotic and antimicrobial use, surface sterilization, air filtration and changes to diet—have changed our internal environment and wiped out important bacteria with beneficial health effects.