There is further evidence for the theory that allergies may be due, in part, from living in environments that are too sterile. Some believe that a certain amount of bacterial exposure is good and makes the immune system act more appropriately. The theory is that immune system, when denied bacteria to interact with, will be triggered by some innocuous substance—hence the allergy.
Children who have been brought up on farms tend to have fewer allergies than other children. A Research Letter in an August, 2002 issue of the Lancet, puts forth the idea that this may be true due to the fact that children brought up on farms are exposed to more microbes.
Exposure to certain bacterial components results in increased expression of the genes that code for receptor proteins. This improves how the immune system achieves its goals, making allergic responses less likely. Lauenerand colleagues found significantly higher expression of these genes in 25 farmers’ children than in 71 children from other backgrounds. They state that this is evidence of a link between exposure to bacteria, and decreased allergy in children who grow up on farms.