Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Effective... But is it safe?

I've only been using this stuff for a couple weeks, along with a new evaporative room humidifier. It seems to be quite effective in keeping any bacteria from building up in the humidifier. The only reason I give this product four stars rather than five is that given the rather scary warnings on the bottle, I am concerned about breathing this stuff in. Also, I'm always petrified when I go to refill the tank that my cats are going to try to drink out of the humidifier's base. I'm thinking that any chemical that is so corrosive that contact with it can permanently damage your skin, as the warning suggests, cannot be too great for your lungs. But then, neither is mold. Until I find a better product, I'm only using this stuff about every third fill.