Most moulds aren't harmful to people without chronic health problems or allergies, but a small amount moulds release toxins into the air that are harmful to even the healthiest people. Molds feed on moisture, and often begin on windows from water leaks or condensation. The key to stopping and preventing mould on your windows and in your home is to control moisture levels in your home and keep windows as dry as possible.
Clean up any existing mould on the window to keep it from spreading. Remove curtains or blinds, cover the flooring and remove or cover any nearby furniture before you start to clean. Use gloves, a cotton mask and goggles, and scrub the mould with a mild detergent. Call in professionals for an area larger than 10 square feet.
Wipe up any wetness or condensation that appears on your windows.
Crack a window to improve ventilation if you notice the windows fogging up or condensation forming.
Replace leaky windows or seal small leaks with window caulk or weather stripping.
Use exhaust fans in rooms where humidity runs high, such as bathrooms, kitchens and laundry rooms.
Make sure vents from your dryer or a gas stove are venting to the outside, instead of the inside of your home. This adds to the humidity and may increase condensation.