Do 24-hour room humidifiers help or hinder asthma sufferers?
High humidity tends to thicken the air you breath and can actually cause breathing difficulties (check out this post I wrote). I also put some tips in this post on how to monitor humidity.
Not only that, but high humidity can be a breeding ground for germs, which may cause lung infections. However, humidity may effect every asthmatic differently, so if you have been around a humidifieir, or the air is humid where you live (like it often is in Michigan in August) and you haven't had any problems with your asthma, then you should be find.
Here are some other links you might find helpful:
7 Everyday Things You Should Avoid Sharing
Is Public Transit Making Me Sick?
9 Ways to Keep Your Airways Clear and Lungs Clean