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Mold Spores

What is mold?

Molds (sometimes called "moulds" or "mildew") are a diverse subgroup of fungi, a classification which also includes mushrooms, yeast, rusts, and smuts. The term "mold" usually refers to fungi that appear as woolly or powdery growths on stored fruits or grow in damp areas of the home (e.g., bathrooms). Although molds are often viewed as food spoilers and causers of plant and human diseases, they, like bacteria, are nature's organic decomposers in the biotic food chain. Molds are also used in the production or certain foods (e.g., bread, cheese, and mushrooms), alcohol, and antibiotics.

Under optimal conditions, a single mold spore can germinate and produce a fungal colony with hundreds of thousands of spores in 4 to 9 days. To grow a fungus requires organic matter and water. The organic matter can be almost any carbon-containing material, such as plant matter, house dust, or paints. Water can be in the form of standing water, condensation, dampness, or high humidity. Fungi can survive in humidity ranges from 0% to 100% but flourish in the 65% to 85% range. Most allergenic molds release their spores into the atmosphere during dry conditions (humidity below 70%); however, some allergenic fungi (certain mushrooms and Ascomycetes) prefer an environment with high humidity for spore release.

Allergy Symptoms and Treatment

Mold allergy is similar to pollen allergy in its symptoms and treatment. However, the growth and spore dispersal of many molds are not as seasonal as that of pollen, and most molds can grow indoors as well as outdoors. People who are allergic to molds may have symptoms that persist for long periods of time, recur several times throughout the year, or are associated with specific environments where molds flourish.

Indoor Mold Spores

Mold colonies may not be large or colorful enough to be seen with the naked eye, but mold growth should be suspected in the following locations:

  • Areas where "musty" or "moldy" odors are detected
  • Areas with poor circulation, such as basements, closets, and other storage areas; closed-up cabins, summer homes or boat cabins
  • Locations where flooding has occurred, especially on rugs and under padding, wood floors, baseboards, paperback wallboard, wallpaper
  • Sites where constant dampness is a problem: leaky plumbing around toilets, under sinks and dishwashers; leaking roofs; poorly sealed basements; inadequately ventilated bathrooms; poorly vented clothes dryers; refrigerator drip pans; air conditioner or dehumidifier condensate reservoirs
  • Indoor house plants and aquariums
  • Stuffed furniture, pillows, mattresses, old stuffed toys, wool carpets, stored paper products (books, magazines), stored clothing and bedding
  • Anywhere dust or soil accumulate in the home

Indoor Mold Spore Avoidance

Fungal colonization and fungal spore densities within the home can be decreased by altering the conditions under which fungi thrive. Precautions include:

Decreasing Available Water

The amount of water available for mold growth can be decreased by repairing plumbing and roofing, sealing basement walls where they contact outside soil, removing plant and leaf litter next to the home, and decreasing indoor moisture. Indoor humidity can be lowered by increasing ventilation; using dehumidifiers, silica gel, or incandescent lights in small rooms, air-conditioning, removing aquariums and indoor houseplants and using home mist vaporizers only infrequently

Elimination of Organic Material

The organic materials on which molds grow indoors can be eliminated or decreased by:

  • Removing dust and soil frequently with standard house cleaning methods (vacuum or wet mop)
  • Removing older stuffed furniture, toys, wool rugs, cotton window coverings and stored paper products
  • Sealing clothing in plastic bags, encasing mattresses and pillows in vinyl, discarding older mattresses and pillows
  • Removing indoor houseplants, wicker baskets, jute and hemp products
  • Using synthetic (e.g. vinyl, plastic) furnishings and textiles for home decoration
  • Cleaning refrigerator drip pans, air-conditioner coils and condensate pans, and dehumidifier reservoirs frequently
  • Changing filters in forced air systems regularly

Use of Fungicides

Fungicides intended for agricultural or nursery use can be used sparingly outside the home with the advice of a nurseryman or agricultural agent. Unfortunately, there are no long-lasting, safe fungicides that can be used inside the home. Common household germicides (e.g. Lysol) ca help kill many indoor molds. Ordinary bleach, at 50% to full strength, can decontaminate basement and bathroom floors and walls as well as other areas where bleach will not damage home furnishings or paint. Special mold retardants are available as paint additives and can be purchased through local retail paint suppliers.

Air Filtration

Air filtration, either as part of an existing forced air system or as a portable single room system, has been shown to be very effective in lowering indoor spore and pollen densities. Two recommended types include high efficiency mechanical filtration or electronic precipitation filtration, either of which can be obtained through local heating and air-conditioning suppliers.

Outdoor Mold Spores

High concentrations of outdoor mold spores generally are associated with certain conditions or situations:

  • The air is relatively free of mold spores in the northern latitudes during periods of freezing temperatures
  • Increased mold spore concentrations can be found in later summer and fall as annual plants die and decomposing leaves begin to pile beneath tress and shrubs
  • High concentrations of Ascomysetes fungal spores can occur during intermittent rains and for 3 to 4 days after a rainstorm
  • Soaring mushroom spore counts will be evident in the spring and fall, 1 to 4 days after a rainstorm
  • High mold spore counts can be found in garden areas, decomposing leaf or plant debris piles, and compost piles, as well as during lawn mowing and raking
  • Elevated mold spore counts can be found in agricultural areas, especially during harvest and around barns, silos, and baled or stacked hay
  • Mold colonies can grow on the north side of a home, on windows next to outdoor plant debris, or on outside walls that are covered by or adjacent to growing plants

Outdoor Mold Spore Avoidance

Exposure to high concentrations of outdoor mold spores can be reduced by:

  • Avoiding piles of leaves and decaying vegetation, gardens, compost piles, and other areas associated with high mold spore counts
  • Removing dense vegetation or plant debris from areas close to outside walls or windows of the home
  • Avoiding lawn mowing or raking
  • Avoiding agricultural areas (especially at harvest time), barns, stored grains and stacked hay
  • Limiting the amount of time spent outdoors during times of high mold spore concentrations, wearing a face mask, if necessary

Contact Information

Allergy and Inflammation - Research
Department of Medicine
Beth Israel Deaconess Medical Center
Center for Life Science, 9th floor
330 Brookline Avenue
Boston, MA 02215