Eat dirt, prevent asthma!

Why have asthma and other allergic diseases gotten so much worse in the last 50 years? No one knows for sure. A leading hypothesis is called the “hygiene hypothesis,” which states that we are too clean. Initially the idea was that we got fewer infections than we used to before immunizations, antibiotics, antimicrobial soaps and gels, etc. However, studies haven’t been able to show, for example, that kids who get antibiotics earlier or more frequently are more likely to get allergic diseases than those that don’t


A new modification of the hypothesis suggests that it isn’t lack of exposure to microorganisms that cause infections that is the problems, but lack of exposure to harmless bacteria and fungi, particularly those that live in the ground. Studies clearly show that growing up on a farm is protective against allergies (as shown in the first graph) and that the more rural the environment the better.

One problem is that measuring the extent of urbanization is difficult. Now, 2 Finnish researchers writing in this month’s Journal of Allergy and Clinical Immunology have come up with a good proxy, use of asphalt. As this graph shows, the increase in asthma in Finland closely parallels use of asphalt.



So if you want to avoid asthma, allergies, etc. eat dirt.

UPDATE: added link to original article. Link to criticism of second graph as misleading.