I did not put it in the run for that reason. I was worried too. So I only put it in the coop. I only used about a half a cup and mixed it really well with the shavings. Once a week I go in there and re-shuffle it around and it works wonderful. But I do think some people on here have had breathing problems with it. I do love the stuff and will continue to use it because IT WORKS. But I will stick with using it sparingly. My one bag will probably last a year! (for your sake as well as the chickens.) just MO.