Quaternary ammonium compounds—usually called quats or QACs—are a large family of chemicals widely used in disinfectants, sanitizers, preservatives, surfactants and other household, institutional and personal-care products. They work. That isn't the question. For No Nines™,...

Pick up the disinfectant spray under your sink and check the active ingredient. If it lists Benzalkonium Chloride, Alkyl Dimethyl Benzyl Ammonium Chloride, or any compound ending in "ammonium chloride," you are looking at a...