March 6, 2008

FeatureSo Clean, It May Cause Allergies

Hand gels are ubiquitous, but should we use them all the time?

We try to protect our children and ourselves. Infants go through a battery of vaccines to keep them and those around them healthy. We wash our hands after touching anything that is dirty. We use antibacterial soaps and seal out germs with airtight doors and windows.

Vaccinations and good hygiene have done wonders for public health, but we might have gone too far. Allergies are on the rise and we may have our extreme cleanliness to blame.

The Hygiene Hypothesis

Researchers are trying to find out why more children have allergies and asthma. The incidence of allergies and asthma is highest in the cities and towns of industrialized nations, but is relatively low in rural areas and developing countries. The cities and towns of industrialized nations are also where vaccinations and germ control are most common. Given these conditions, scientists have started to link allergies and asthma with cleanliness.

“It’s called the hygiene hypothesis,” says Marc McMorris, M.D., a pediatric allergist at the University of Michigan Health System. “We’ve developed a cleanlier lifestyle, and our bodies no longer need to fight germs as much as they did in the past. As a result, the immune system has shifted away from fighting infection to developing more allergic tendencies.”

Asthma and allergies are on the rise. Could the lack of germs in our environment be the cause?

Idle Immune Systems

Certain viral diseases, such as chicken pox and mumps, used to be childhood rites of passage—every child contracted the illnesses. Parents would even host chicken pox parties to expose a group of children to an infected child. That might seem malicious, but the parents knew their own children would get chicken pox eventually, so why not let their child be exposed to the virus sooner rather than later.

Children also came into contact with bacteria, parasites, and scores of other viruses that kept their immune systems active. Their bodies faced an onslaught of invaders and their immune systems responded in textbook fashion. Special immune cells would target invaders then retreat to fight another time.

Over the past 30 years, children in the United States, western Europe, Japan, and other industrialized regions have faced far fewer invaders. There are vaccines for chicken pox, mumps, and other childhood illnesses. Children commonly use antibacterial wipes and soaps in bathrooms, kitchens, and even vehicles. People wash their hands after, well, just about anything—using the bathroom, making a meal, a trip to the petting zoo, even a trip to the grocery store.

“The natural immune system does not have as much to do as it did 50 years ago because we’ve increased our efforts to protect our children from dirt and germs,” says McMorris. Because the immune system has less to do now than in the past, it is no longer preoccupied with a potentially deadly invader. Instead, the immune system reacts to foreign substances in the environment: pollen, dust, fabric, and even food.

This girl is suffering from hives, an allergic reaction.

When More Equals Less

A now-classic study looked at the incidence of allergies in farm families living in eastern Europe. Researchers found that when the families live in close proximity to animals, the number of reported allergies remained low. There seemed to be a correlation between increased exposure to farm pathogens and dirt and a lower incidence of allergies and asthma. These findings provided a compelling argument for the hygiene hypothesis.

Scientists are finding more evidence for the hygiene hypothesis at home, literally and figuratively. Today’s families have less than three children on average, which limits exposure to germs and infections. Children from larger families tend to exhibit fewer allergies while they are simultaneously exposed to more bacteria and viruses. Children that stay at home, rather than attend daycare, also tend to have more allergies and asthma because they too are not exposed to as many bacteria and viruses. Children in daycare may get sick more often in the first few years of life but they also tend to have fewer allergies.

The hygiene hypothesis is far from a theory, though. More long-term experiments are needed to determine the exact correlation between a super-clean society and the rise in allergies and asthma. Scientists also need to pinpoint why the immune system reacts to allergens so strongly and for so long, especially when it isn’t fighting off as many pathogens.

Let Kids Be Kids

McMorris concedes that it can be hard to find a balance between being clean and being too clean. “We all try to do our best with our children,” he notes. “We certainly should not step back in time and stop immunizing our children against deadly diseases. But we should use more common sense. While we should keep our houses clean, we need to be diligent about changing our furnace filters and keeping allergens like mold out of attics and basements.”

While it is good advice to keep allergy and asthma triggers out of the home, it is also good to let kids be kids. In most cases, children will do just fine when exposed to dirt and germs on the playground, at the zoo, at the grocery store, and out in the backyard. Dirt will wash off in the bathtub and a few germs could give an immune system a workout. Let kids make mud pies with a friend sporting a runny nose—it could help keep allergies at bay!

More to Explore

• Human Reaction To Spotless Lifestyles
• The Hygiene Hypothesis: Are Cleanlier Lifestyles Causing More Allergies For Kids?
• Hygiene Hypothesis: Fact or Fiction
• Hygiene Hypothesis (video segment)

What Do You Think?

Last updated March 6, 2008 | Comments (19) | Permalink | Feature