It's complicated, but the science is fairly well established that lack of parasitism has lead to increased incidence of allergies in developed nations. Small price to pay.
We are rapidly approaching an era of medical treatments where giving a treatment of "probiotics" to correct your newborn child's gut bacteria in order to prevent asthma much the way we give immunisations against diseases today. The hygiene hypothesis is getting some pretty compelling evidence and hopefully it will lead to us learning the "right" kind of things we should be exposing our children to in order to prevent these autoimmune conditions.