Peanut allergies on the increase

A survey report in the Journal of Allergy and Clinical Immunology says that peanut allergies have tripled in the last decade.  Why?  The authors don’t really know although they speculate that children aren’t exposed to as much dirt as they used to be.

Are we really that much cleaner than we were 10 years ago?  I doubt it.  But I would very much like to know why this is happening.