How often you have your carpets professionally cleaned depends on a number of circumstances. Du Pont, the world's largest manufacturer of fiber, recommends cleaning at least once every eighteen months. But other considerations may increase the frequency rate: smoking habits, number and age of children, soiling conditions, humidity, temperature, condition of the outdoor environment, health status of occupants, allergy conditions, number and types of pets, and the types of activities being conducted are just a few considerations.