Proof that Early Exposure to Germs is Good for You

Children are acquiring serious allergies and autoimmune in increasing numbers in developed countries. Allergies are rare in undeveloped countries. Children on farms seldom have allergies and the children in families
with more pets have fewer allergies. These findings have been explained by the "Hygiene Hypothesis": Early exposure to germs and allergens (molecules that can cause an allergic reaction) will cause the body to develop appropriate immune responses
. So far the Hygiene Hypothesis was based on statistical associations, now an experiment in piglets directly links exposure to a dirty environment in early life to a healthy gut environment and expression of immune genes (Mulder et al.).

In the pig study, 54 piglets were divided into three groups, one group went to live outdoors, another group was housed indoors and a third group was isolated and given antibiotics daily. The intestines of the outdoor group ended up with a more favorable composition of microbes in their intestines than the two indoor groups. For example, lactobacillaceae, which help to get rid of disease-causing bacteria, were a lot more plentiful in the gut of the outdoor pigs. The difference in gut microbial composition was also linked to the expression of genes involved in immunity. Infection-fighting genes were activated in the outdoor pigs and genes involved in inflammation and cholesterol synthesis were highly expressed in the indoor pigs.

The researchers of the pig study conclude: "Early-life environment significantly affects both microbial composition of the adult gut and mucosal innate immune function" (Mulder et al.). Although pig intestines and immune responses may not be identical to those of humans, pig organs are similar in size and the types of microbes residing in pig intestines are similar to those found in human intestines.

The hygiene hypothesis proposes that children will develop allergic and autoimmune diseases in later life if they are not exposed to infectious microbes or allergens in early life. In contrast to popular belief,
pollutants do not to appear to increase allergies and immune disease according to a study done by Dr. von Mutius with East German and West German children right after the Berlin wall fell. East Germany had a highly polluted environment compared to West Germany, but the West German children had more allergies and autoimmune disease. Although antibiotics and clean living may protect children from deadly infections in developed countries, they may also prevent the development of a healthy immune system.