Perhaps it's no surprise that as the product-information revolution plays out, the net effect of the vast array of opinions (from experts, from advertisements, from online reviews, from other consumers) means that sometimes we are simply unsure whom to trust. If you feel the air around you is unclean, and a gizmo comes along that says it will help, maybe you go with the recommendation that seems most hopeful.

Perhaps my blog would be more widely read if I made an effort to be hopeful.

As Asher notes, Consumer Reports's medical consultants say most people do not need any of these devices. "So," he says, "the bigger issue could be, why are people buying air cleaners at all?" At a time when consumer choice may be more confusing than ever, the magazine can give people an assessment that has no commercial bias, he concludes, "but we can't make their decisions for them."