Since moving to Finland, I’ve become accustomed to asking guests whether they have any allergies before I prepare dinner.  I grew up in the developing world where allergies and asthma seem to be much less common than they are here; in fact, various studies have found higher rates of allergy and autoimmune conditions in developed than developing countries.  One explanation for this is the “hygiene hypothesis“, which proposes that excessive hygiene early in life can affect the development of the immune system and result in allergic conditions and autoimmune diseases in later life. In a recent study appearing in Science, a team of scientists in Germany and the United States present evidence supporting the hygiene hypothesis and the importance of an early challenge to the immune system.
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