The Hygiene Hypothesis: Is Cleanliness Next to Sickliness When it Comes to Asthma and Allergies?

Twelve-year-old Micah had his first and only ice cream as a baby. He was 10 months old, and his grandmother let him have just a taste from an older brother’s dish. “He turned bright red, broke out in hives, and began this wet wheezing, like he was drowning,” recalls his mother, Vicky Enriquez. Fortunately, there was a hospital just a few blocks away.

Today, Enriquez knows that Micah – but not her other three children – is allergic to milk, eggs and soy products. He also has asthma. The family now specializes in reading food labels, and has an inhaler in every car. They know which fast-food restaurants use egg in their hamburger buns and have an understanding with their local pizza parlor about the true meaning of “no cheese.”

The U.S. Centers for Disease Control and Prevention (CDC) reports that there are more kids like Micah every year – kids who have allergies, asthma or both. But asthma and allergy rates aren’t the same everywhere.

“It’s highest in our ultra-urban modernized cities,” says Dr. Andrew Liu, an associate professor in pediatric allergy and clinical immunology at the National Jewish Medical and Research Center. Dr. Liu is one of several researchers trying to find out why.

There’s a growing body of evidence that the increase in allergy and asthma could have something to do with our modern tendency to like things super clean. Known as the “Hygiene Hypothesis,” this theory suggests that all this sanitation keeps us from being exposed to natural substances that help us develop normal, healthy immune systems.