Mold and mildews are harmful at least to the materials on which they grow, and they usually produce objectionable odors, stains and discolorations. If mold conditions are allowed to exist for long in a wood structure, the wood can quickly become weak and rotten. Fabrics and paper can be seriously damaged or destroyed in days by damp, moldy conditions. If molds grow extensively, they may produce enough airborne irritants to cause coughing and cold-like symptoms. Allergic persons may react to very small amounts of mold.
Mold needs to have moisture on which to grow.
In most cases household mold is due to moisture problems. Mold also needs food and nutrients. Most materials found in homes will support the growth of mold and mildew if they become damp. Generally it is not necessary or helpful to test molds found in homes. Usually damp areas in homes will have a large number of molds growing together.