The Hygiene Hypothesis Definition, Information - MedicineNet
The key to understanding how the hygiene hypothesis might explain the high level of asthma in developed nations (and perhaps a number of other diseases such as Crohn's disease, ulcerative colitis, or multiple sclerosis) is knowledge of how the immune system develops, matures, and self-regulates. Although the details of the development and function of the immune system can fill books, a very brief summation is as follows: