On Being Too Clean

I was first introduced to this concept several years ago. I read and article that talked about the fact that the polio virus had been around for ages, but the disease never became a dreaded epidemic until the 20th century. The person writing the article said that through out history babies had been exposed to the polio virus very early due to the general lack of sanitary conditions. The young babies still had some immunity that they had acquired from their mothers, who had also been exposed at an early age. This helped to mitigate the effects of the polio. When the sanitation of the early 20th century came along, this cycle was broken. Babies did not contract polio early. Later when they did get it, they had no natural immunity and were affected much more dramatically.

Today I read this article. Intestinal worms beneficial? Maybe we can be too clean.