Germ exposure may keep your kids from developing allergies

Healthy child - April 2005


Dr. Alyna Chien


Parents become frustrated when their child seems to go from one cold or stomach bug to another, especially in the first year of life. Germs appear to be the enemy and parents do everything in their power to eliminate them.

The fact is, the average child can have four to six illnesses in the first year of life and two to three each year after that. The illnesses afflicting today’s immunized and otherwise healthy children are more hassles than life-threatening diseases. Even though it doesn’t feel like it in the middle of the night, the majority of today’s children make it through these colds and flus on their own with a healthy dose of tender loving care from their parents. 

That’s not to say we shouldn’t protect our children from the spread of disease. Like many parents, I have done my share of trying to keep my child from getting sick. I’ve sterilized bottles (for pumping), put toys in the dishwasher and cringed when strangers touched my babies’ hands.

Although I never got into the antibacterial soaps or wipes, I did enforce strict hand-washing practices before meals. Some may even consider me lax because I do allow my kids to apply the “10-second rule” for eating food that falls to the floor (although the desire to eat things off the floor only seems to apply to snacks and candy).

According to some research, there may be reason to relax the vigilance we hold against germs and infections. There is some evidence that a greater number of colds and diarrheal illnesses early in life may actually protect against the development of allergic diseases such as eczema, hay fever or asthma later on.

This theory, called the “hygiene hypothesis,” seeks to explain why allergic diseases have risen dramatically while serious infectious diseases—such as the flu—have dropped significantly over the past few decades.

Germs as teachers

Germs—and other things—enter our bodies through every breath we take, constant invisible breaks in our skin and all the things we eat. But before our immune systems can attack the germs, it must distinguish harmless invaders (such as dust, mold and cat hair) from harmful ones (such as germs). The immune system begins developing this ability when the child is still inside the womb, but many believe this continues through the first few years of life.

Some now wonder whether our modern successes over germs have robbed our bodies of a key player in the development of our immune system. The “hygiene hypothesis” suggests that in a germ-free situation, the immune system has nothing to fight against and is left to generate immune responses to benign things, leading to allergies.

Several studies have shown that infants with more siblings have more upper respiratory infections. But these children are also less likely to develop hay fever, eczema and asthma as older children. The same has been shown to be true for infants and toddlers in daycare—these children have more infections early on, but seem to have fewer allergic diseases in grade school.

Children living in a farm setting who were exposed to more germs early in life, as well as kids who developed certain gastrointestinal infections at an early age, were also less likely to develop allergies later in life.  

Hygiene still important

Despite this rather convincing evidence, there is still a lot to learn about the role germs and infections play in the development of allergies. We don’t know which is more important—the timing of the infections, the quantity or both. We don’t know if the type of germ matters—we’ve only studied the ones that cause colds and diarrhea in children.

The relationship between infections and allergies remains complicated. For example, once the immune system revs up to fight allergic diseases, the body has more difficulty fighting other infections. So, while a healthy child with an influenza infection would probably stay in bed for a week, an asthmatic child with the same infection might need to be hospitalized.

While science sorts out how the immune system works, it is important to remember that, in general, common allergic diseases are much less harmful than the infectious diseases that afflicted our parents’ generation. Immunizations remain the most effective way to protect a child from infectious diseases that used to lead to permanent damage and death—and still do in countries that lack widespread immunization programs.

Basic hygiene, such as hand washing, remains important for minimizing the spread of disease, but avoiding every germ possible is probably not necessary or important. In the vast majority of cases, it is OK for otherwise healthy, immunized infants and toddlers to have a minor illness—cold, flu or diarrhea—every two to three months.

Finally, the next time you’re up in the middle of the night with an uncomfortable child, embrace the idea that the illness is actually helping your child’s immune system develop and may play a role in keeping him from developing allergies.


Alyna Chien is the mother of two, a pediatrician and a Robert Wood Johnson Clinical Scholar at the University of Chicago’s Department of Pediatrics.

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