Windows should be professionally cleaned at least once per year, depending on the amount of traffic and weather in your area. Exposure to direct sunlight can find windows richly concentrated with dust and dirt, which can lead to wear over time. Some guidelines recommend cleaning windows more often if you live in an industrial area or outside the city where there is a lot of air pollution. Windows inside homes are also susceptible to household damage like smoke from cooking that may require more frequent cleaning than exterior view windows. In all cases, it’s best to discuss frequency with a professional for your specific need!