This is a catch-22 I'm sure not all Air Purifiers are good for your health but with all the new and advanced technology out there a lot of them are very good for your health. Now you can kill mold and mildew and all kinds of contaminants. Your best bet to find an answer for this question would be to research all the new air purifiers out there.
A great website with information on Air Purification is http://www.clean-air-today.com
They review a lot of the new units out there and have a lot of helpful information.