Can We Be Too Clean for Our Own Good? The Hygiene Hypothesis Reviewed.

The hygiene hypothesis began as an attempt to explain the relatively rapid rise in atopic diseases. Strachan's early hypothesis regarding the role of family size and exposure to early childhood infections in the development of atopic diseases has clearly evolved to integrate the possible effects of hygiene, eradication of parasitic infections, immunizations, improvements in home heating and ventilation, dust mite exposure, breastfeeding duration, diet, parental smoking, pollution, and exposure to pets and farm animals. However, as most of our understanding at the current time still comes from observational and epidemiologic studies, further investigations are needed to help uncover which of these genetic and environmental factors are indeed the causes behind the increases in allergic rhinitis and asthma.