Common Mold vs. Black Mold

A woman looks at mold.

Virtually everyone has some mold in their home. Although not all types are toxic, even exposures to non-toxic mold types pose health risks such as allergies and asthma. It is often difficult to distinguish types without lab testing. Black mold, which is toxic, should be cleaned and removed immediately.

Common Mold (Non-Toxic)

The black mold that you may see growing on grouting and walls of showers and bathtubs is unlikely to be dangerous. The most common mold is Cladosporium. Although it can be an irritant to those with asthma or respiratory disease, it is not known to pose any toxic hazards. It can be removed with various household cleaners and bleach. The most effective way to prevent it is by providing adequate ventilation. Vent fans should be installed in all areas where dampness can occur.

Black mold growing on tiles and grout can be treated with bleach (a cup to a gallon). Saturate the area for approximately 15 minutes, then wash with a strong detergent. The area must then be thoroughly dried. The bleach will kill the mold, but may not remove all the dark pigments associated with it.

Toxic Black Mold

Black mold in the corner of a room.

Black mold and toxic mold are common terms used to describe a greenish-black substance which can result in a very serious health risk. While toxic black mold is less common than other mold species it is far from rare. Cellulose is the only known host for the dangerous strains of Stachybotrys and Memnoniella, which produce mycotoxins. The mycotoxins grow in damp areas.

Substances where this mold can be found include places where water has soaked wood. Ceiling tile, wall paneling, studs, cellulose insulation, drywall, carpet backing, cardboard, and other items made of natural fibers such as cotton can act as a host. It can infest areas in the floors, walls, and ceilings. Mold problems resulting from flooding should be treated professionally to avoid health risks. If the black mold is growing on materials that do not contain cellulose, it is unlikely that either Stachybotrys or Memnoniella are present. If you suspect black mold, have it tested before attempting to remove it.

Clean Dried Mold

A woman cleans mold.

Spores from dried mold are very dangerous and should be cleaned with caution. Never scrape or scratch dried mold, because the spores will become airborne and create a serious inhalation risk. A respiratory mask and eye protection are necessary, as is adequate clothing to prevent skin contact. Most mold infested areas are relatively small and are usually the result of small leaks or plumbing problems. If the problem is internal such as on insulation or throughout a carpet, the only solution is to have the items professionally removed before being replaced. Moldy areas more than two feet in size are considered "heavily infested." In these cases, professional removal is strongly advised. Some insurance companies cover the cost of mold removal or remediation under certain circumstances. Check with your insurance agent to find out if you are covered.

Prevent Black Mold

In order to prevent black mold, you should keep the humidity level in the house below 40 percent, use an air conditioner or dehumidifier during humid months, and be sure there is adequate ventilation, like exhaust fans, in kitchens and bathrooms. You should also add mold inhibitors to paints before using them, clean bathrooms with mold killing products, remove and replace previously soaked carpet and upholstery, and refrain from using carpet in bathrooms and kitchens.