Mold can grow quickly in humid areas with a lot of moisture and limited airflow. If you're worried about your purifier growing mold, try using it in a dry room, and avoid using it in rooms that tend to retain moisture, like the bathroom. You can also remove the filter from time to time to check for mold and clean it as needed. If you live in an area where it's difficult to manage humidity, consider using a dehumidifier. Not only will it decrease the chances of your purifier growing mold, but it can make any room more comfortable.