Is the increased prevalence of asthma and allergy in the younger generations because parents kept them too clean?
Not exactly. One factor at home can be that we drop our sandwich in the floor (or dirt) and immediately throw it out. In years past we would dust if off and eat it anyway. Such exposure to micro-organisms stimulates the immune system. The hypothesis suggests less of these exposures(going overboard with purel etc) may prevent the immune system from "getting a workout" and being as strong.