The Hygiene Hypothesis

The hygiene hypothesis was first proposed in 1989, suggesting that the increase in allergic diseases seen in the western world over the last 50 years is a consequence of increased cleanliness1. Increased cleanliness results in reduced exposure to infectious agents and allergens in early childhood. It is believed that exposure to allergens within the first year of life promotes T-Helper 1 (TH1) response when encountered again later in life, whereas a T-Helper 2 (TH2) response is favoured if the first encounter occurs after the first year of life. The TH2 response stimulates B-cells to release immunoglobulin E (IgE), which has been attributed to the symptoms of allergy2. Whilst this hypothesis has proved highly controversial and sparked many a debate, it still remains unclear whether increased cleanliness is linked to an increased susceptibility to allergens.
Riedler et al.3 reported results on 812 European children, from both farming and non-farming households. Previous studies had shown that endotoxins were found at higher concentrations in farm houses compared to non-farm houses4. Participants completed a questionnaire, detailing allergies that their children had, and their child’s exposure to stables and farm milk within their early childhood. Furthermore, blood serum samples were collected for analysis. Serum IgE response to selected allergens, including pollens, microbes and other infectious agents, was measured. They found that children who were exposed to farm life in their first year of life were less likely to have reported allergies, and also less likely to have positive serum IgE results. In farm exposed children, 1% were diagnosed with asthma, and 12% with atopy, compared to 11% and 29% in non-farm exposed children. T...

... middle of paper ...

... iss. [online]. Available from: http://www.imvs.sa.gov.au/wps/wcm/connect/aa1661c3-a08a-48ee-86da-d66e6ff4d7ca/allergens-interpreting-results.pdf?MOD=AJPERES [Accessed: 5 March, 2014]
6) Perzanowski, M.S., Ng’ang’a, L.W., Carter, M.C. et al. (2002) Atopy, asthma, and antibodies to Ascaris among rural and urban children in Kenya. J Pediatr, 140(5):582-588
7) Brooks, C., Pearce, N., Douwes, J. (2013) The hygiene hypothesis in allergy and asthma: an update. Curr Opin Allergy Clin Immunol, 13(1): 70-77
8) Schaub, B., Liu, J., Hoppler, S. Et al. (2009) Maternal farm exposure modulates neonatal immune mechanisms through regulatory T cells. J Allergy Clin Immunol, 123(4): 774-782
9) Nembrini, C., Sichelstiel, A., Kisielow, J. et al. (2011) Bacterial-induced protection against allergic inflammation through a multicomponent immunoregulatory mechanism. Thorax, 66(9): 755-763