The hygiene hypothesis provides an explanation for the sharp increase in atopy over the past several decades by proposing that it is inversely related to the lack of infectious diseases in our society. Although atopy, as well as other hypersensitivity reactions, do have a genetic basis; studies clearly show that environmental and socioeconomic factors play a large role in determining which people will develop allergies. Proposed mechanisms leading to this disorder include an imbalance in the Th1/Th2 complex in the immune system, and a deficiency in Regulatory T cells which controls excessive T cell activity.
Tropper, Y. (2015). Understanding the Hygiene Hypothesis and its Mechanisms. The Science Journal of the Lander College of Arts and Sciences, 8 (2). Retrieved from http://touroscholar.touro.edu/cgi/viewcontent.cgi?article=1066&context=sjlcas