The individual mold spores are flowing throughout the open air all of time. When the small amount of spores are breathed outdoors they are combined with such a large portion of fresh are that they rarely have an effect. Sometimes in the spring the outdoor counts increase an create outdoor allergies. However when moisture is aloud to dwell on a porous surface inside a building these few mold spores will attach themselves to that surface and begin to grow at a rapid pace. Once these spores have attached it takes much more than household cleaners to break there strong hold.