A study published in Nature have shown that chitin, a compound that makes up the exoskeletons of insects, worms and crustaceans triggers an allergic inflammatory response in the lungs of mice, as well as increased production of the chitin-destroying enzyme made by cells lining the lung airways. This finding in itself may not be unexpected, as chitin is after all, a foreign material. However, these results support the "hygiene hypothesis" which attempts to explain why asthma and other allergies have greatly increased in many industrial nations.

The hypothesis holds that modern societies have largely cleaned up living conditions so that people are exposed to far less dirt and all of its organic constituents. At the same time, antibiotics and microbicides have reduced the numbers of microbes in the environment. Bacteria are known to degrade chitin, and Locksley suggests that the reduction in bacteria may lead to an increase of chitin in the environment - largely from molds and insects -- perhaps explaining the findings from several studies that the highest childhood asthma risk tends to be associated with the lowest exposure to bacteria.

Makes sense, I guess. But then, humans can produce chitinase to degrade chitins, so accumulating chitins in the environment shouldn't be a problem, right? Or are the levels perhaps too high for our bodies to cope with?