In advanced countries the incidence of allergy is twice that of less developed countries. Various studies suggest that in the attempt to make the places where we live clean, we interfere with the optimal development of the immune system. Exposure to certain germs in our first years of life would actually be useful for the immune system to later distinguish between friend and foe. Today’s indiscriminate war against all germs does not allow this distinction to be made. Without adequate training our immune response attacks a host of harmless targets such as pollen and dust mite.