I have read that all de is bad to breathe in but I think it's more along the lines of people who work with it on a daily basis and breathe it in constantly, but I could be wrong. It is basically like little shards of glass that can supposedly irritate your lungs. I don't know if it actually does anything for bugs, I have it sprinkled liberally on my concrete basement windowsill and there's still live fruit flies on my plants down there. Grrr. Also, people mix it in with their livestock feed to control insects and parasites and the animals breathe it in as they're eating, they have to, they stick their nose right in the food. Nobody has ever mentioned that.