Molds and mildew will grow wherever moisture and nutrients exist together. Outdoor mold can be found in shady or damp areas. Common places mold and mildew grow outdoors include:

• Leaves and vegetation
• Rotting logs, twigs and bark
• Grasses, trees, bushes and flowers
• Soil, sand, dirt and dust
• Animal carcasses and feces
• Hay, straw and feed
• Compost heaps, mulch piles
• Grains (e.g., wheat, oats, corn)
• Construction areas

Mold spores ultimately enter a home or building from the outside through doorways, windows, heating ventilation and air-conditioning systems with outdoor air intakes. People and pets also carry mold spores in from the outside. Spores easily attach themselves to clothing, shoes, bags, hair and fur. Mold or mildew will grow when these spores fall in places where there is sufficient moisture and nutrients.

While there are hundreds of thousands of molds that thrive outdoors, fewer are found indoors. Common indoor molds include:

• Alternaria (also common outdoors)
• Aspergillus
• Aureobasidium (Pullularia)
• Bipolaris (also common outdoors)
• Cladosporium (also common outdoors)
• Epicoccum (also common outdoors)
• Fusarium (also common outdoors)
• Helminthosporium
• Mucor
• Penicillium
• Rhizopus

Stachybotrys chartum (Stachybotrys atra) is less common, but not rare. This mold is most commonly associated with the terms “toxic mold” or “black mold,” although other forms of mold may also be called by these names.

Indoor mold can be found throughout a home or building in areas such as:

• Bathrooms
• Kitchens
• Basements
• Closets
• Walls
• Garages
• Attics
• Window moldings
• Air–conditioning ducts
• Storage areas
• Laundry rooms
• Crawl spaces
• Garbage cans
• Refrigerators
• Barns
• Greenhouses
• Saunas
• Houseplants

Because mold and mildew will grow where moisture exists, it can be found in every home or building in any climate. Water may accumulate within a home when ventilation is too poor to expel moisture produced by common activities like showering, cooking, washing clothes and cleaning.

Although molds thrive where water usage is common, high moisture levels can exist anywhere in a home as a result of water leaking from pipes, ducts, plant pots or appliances. Water may also enter a structure from the outside through the walls, floor or roof if the home or building is weak or damaged.

Flooding or poor drainage is a common cause of unwanted moisture in the home. Moisture in carpeting and upholstered furniture, for example, can produce mold (and allergens) in less than 48 hours because these materials have nutrients that encourage mold growth. Examples of other materials that may encourage mold growth when wet include:

• Wood
• Paper
• Cardboard
• Ceiling tiles  
• Paints
• Wallpapers
• Insulation materials
• Drywall
• Fabric
• Mattresses
• Pillows
• Window moldings