A new study suggests that the health benefits of exposure to allergens and germs are most significant in the first year of life. Which raises the question: should you roll your baby around in mouse hair?*

Researchers studied 560 children with a high risk for asthma over the course of three years.** Participants in the study were given yearly examinations and their homes were tested for cat, dog, cockroach, mouse, and dust mite allergens. Additionally, bacterial samples were collected from 104 homes.


The study found that the greater cumulative exposure children had to cockroach, mouse, and cat allergens, the higher the risk for wheezing and sensitivity to allergies. By age 3, 44% of children were sensitized to at least one allergen and 36% had recurrent wheezing (a possible sign of asthma).

None of that is surprising and it dovetails well with our prior knowledge about the interaction between environmental factors and asthma. The study's significance lies in the timing of exposure. Children with high exposure to cockroach, mouse, and cat allergens as well as specific bacteria in their first year were less likely to exhibit recurrent wheezing. Only 17% of children exposed to the allergens during their first year had recurrent wheezing compared to 51% of children exposed to no allergens.

Further research is needed, but this finding certainly indicates that earlier exposure is protecting against asthma and allergies. What do we do with this information? Hopefully it will inform preventative strategies moving forward. They should probably come up with something more productive that "cover your child in cockroach allergens."

The Hygiene Hypothesis posits that there is a benefit to mucking around in the dirt and exposure to bacteria as a child. The increased rates of allergies and asthma are believed to be connected to the cleaner environment we live in - a world of Purell and foam floored playgrounds. Essentially, our immune systems previously focused on protecting us from bacteria and other pathogens, allowing a natural development of the immune system. Now that we have reduced exposure, children fail to develop immune tolerance and turn attention to previously benign parts of our environment such as allergens leading to allergies and asthma. The findings presented here support this hypothesis but narrow its influence to the first year of life. Maybe we should pull back a little on the obsessive vacuuming/santizing/obsessive cleanliness of our environment***. I say this as someone who never leaves the house without a bottle of Purell.

*No. The answer to this is no you should not.

**Children in major urban areas (in this case Baltimore, Boston, New York, and St Louis) are viewed as high risk for asthma due to environmental exposures. Air pollution is a major contributing factor in the development of wheezing but was not examined in this study. These elements also impact the difference in rates of asthma amongst communities of differing socioeconomic statuses.

***To be clear, I'm not suggesting this in hospitals, etc