If you use a cool mist humidifier to make your home more comfortable, CLEAN the humidifier weekly. Use white vinegar first to remove scale (lime) build up. Then put about a quarter cup of regular household bleach in the base of the humidifier and add hot water to a level above the ordinary fill line. let sit for 15 to 20 minutes, pour out the bleach water and rinse thoroughly. When working as a Respiratory Therapist some 35 years ago, I helped care for a young boy who came in with some weird respiratory infection. His mom brought in the cool mist humidifier she ran in his bedroom. The therapist who filled it was shocked to find the water turned pink when she filled it with sterile water. It was full of any number of nasty microbes and the microbes were being flung into the air and inhaled by her child.