Updating the Hygiene Hypothesis

From  The New York Times  on June 3rd, 2016 – Educate Your Immune System


This article summarizes recent research done on the development of autoimmune diseases (Type I diabetes, celiac disease, severe allergies, etc.) in children who grew up in different microbial environments – represented by households in Finland, Estonia, and the Karelia region of Russia. Studies found that, when factors such as diet and breastfeeding were controlled for, toddlers  who grew up in Finland were four times as likely as those in Karelia to develop precursors for Type I diabetes, and the two groups had very few similarities between their microbiomes. Karelia is a significantly poorer area than most of Finland, and many households drink untreated well water, so researchers hypothesized that early exposure to microbes from the environment “taught” the toddlers’ immune systems how to respond appropriately to common environmental pathogens, and so they developed fewer autoimmune issues.


We’ve discussed acquired immunity in class, but this area of research takes it a bit farther, and suggests that our microbiomes and  when we are exposed to certain microbes may play a larger role in our immune development than previously thought. Other studies mentioned in this article found that children who were exposed to certain pathogens at a young age were much less likely to develop autoimmune diseases than those that first encountered the same pathogens as teenagers or adults. This updates the hygiene hypothesis (which I think we discussed briefly?), which essentially says that people exposed to fewer kinds of microbes during their development tend to be sicker than those that were exposed to a wider variety of microbes.

Critical Analysis:

I appreciated  the angle this article took, describing autoimmune diseases and decreased exposure to diverse microbial communities as an issue of the 21st century. The author did an excellent job of defining terms and ideas that may be foreign to the lay reader, and I think this article is accessible to a wide range of audiences. However, the article implicitly assumed that the relationship between early microbial exposure and autoimmune disease was proven, and I don’t think any of the studies examined in the piece proved a causal relationship. Popular science writing needs to be careful not to assume causation when it has not been proven!


How might we (ethically) prove a link between childhood microbial exposure and autoimmune disease?