We carefully watch what goes into our mouths and on our bodies—organic this, petroleum-free that. But when it comes to keeping a healthy home, knowing what to do isn’t so easy. In fact, the average house may contain as many as 400 chemicals, some of them toxic, many untested, according to a 2009 study in the journal Environmental Science & Technology. Short-term contact with one toxin in small amounts isn’t going to kill you. But with so many questionable chemicals swirling around us, “you definitely want to take simple measures whenever possible to lower your exposure,” says Phil Brown, PhD, director of the Social Science Environmental Health Research Institute at Northeastern University in Boston.