Asthma Severity and Prevalence: An Ongoing Interaction between Exposure, Hygiene, and Lifestyle

February 2005 | Volume 2 | Issue 2 | e34 Over the last hundred years, there have been major triumphs in medicine related to public health, vaccination, and the introduction of new medicines. However, over the same period, several diseases have increased in prevalence and/or severity. In some cases, the causes of the increase have become obvious—the increases in lung cancer, coronary artery disease and type 2 diabetes, for example, are not considered to be a mystery. On the other hand, a large group of diseases related broadly to “infl ammation” have also increased. For these, a wide range of hypotheses about causation have been proposed. Type 1 diabetes, rheumatoid arthritis, and infl ammatory bowel disease have increased since 1980 [1]. Some analyses of the increase in hay fever and asthma would suggest a similar time course, and this parallelism of the time frame has been taken to suggest that there could be a common cause. Indeed, there is a proposal that these diseases are all related to some changes in “cleanliness” or “hygiene” that have resulted in decreased activation of a common control mechanism. Specifi cally, this control has been ascribed to T regulator cells, which produce interleukin-10 (IL-10) or transforming growth factor-beta.