Mold is alive, but it is neither a plant nor an animal. Mold is a type of fungus. It is part of a group of living organisms that are very common and serve an important role in the environment. Penicillin, an antibiotic that has saved many lives, is a type of mold, as is yeast.

However, mold can grow on bread and other types of food, making it unfit to eat. Mold can grow on the walls, floors and ceilings of your home as well as on your personal possessions. People often refer to some household molds as mildew, although the term also can apply to molds found outdoors.

Mold spreads by creating reproductive cells called spores and sending them into the environment. Mold spores are too small to detect with the naked eye. They are everywhere around us and you cannot avoid being exposed to them. Mold spores travel in the air and attach to people's skin, clothing, shoes, shopping bags and belongings. Other ways spores can enter your home invisibly are:    through open doors and windows    through your home's heating, ventilation and air conditioning system    on the fur of a pet Once spores enter, they can settle onto carpeting or other surfaces inside your home. You cannot keep spores out of your home, but regular home cleaning and maintenance often can prevent mold problems before they arise.