About Household Mold and Mildews

Mold and mildew are simple, microscopic organisms that can grow virtually anywhere if they have adequate moisture, nutrients and appropriate temperatures. Depending on the particular mold or mildew, growing colonies can be almost any color from white to black. Most household molds and mildews are black, grey, or charcoal colored. Spores of dozens of kinds of mold and mildew are present at all times in indoor and outdoor air. These spores can settle, germinate and grow wherever good growth conditions are found. They can grow on soil, plants, dead plant materials, foods, fabrics, paper, wood and many other materials. Most molds are not harmful. In fact, molds have important roles in the environment and in living systems. In soil molds play a crucial part in decomposition of organic matter and in making nutrients available to plants.

Molds and mildews can be very destructive to materials on which they grow, and are usually unwelcome and unhelpful in homes. They cause staining, decomposition (rotting of materials) and objectionable, musty odors. Where colonies are extensive they can also produce enough spores, and by-products to be harmful to health. Many of the by-products of mold and mildew are irritating to skin, eyes and respiratory tracts. Some molds produce true allergic sensitization and allergic reactions in susceptible people. Some molds produce toxic by-products that could be harmful to skin, and poisonous if ingested or inhaled in quantity.


Should I be concerned if I have mold or mildew in my home?

Yes. 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.


What conditions produce mold and mildew in homes?

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.


What are some conditions that cause or aggravate mold?

Flooding, leaking water pipes or fixtures, backed-up or faulty drain plumbing, leaky roofs, use of humidifiers, extensive use of hot water indoors (laundering, cooking, bathing) without adequate exhaust venting for steam, damp basements or crawlspaces, houseplant water or aquarium leakage, indoor clothes drying, and unvented combustion appliances are all important sources of indoor moisture, and can encourage mold growth. Heavy condensation ("sweating") of windows, exterior walls or other cold objects indicates excessive moisture and inadequate venting.


Should I test for mold or have mold samples from my home tested?

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. Even though many molds produce toxic or potentially toxic substances, merely finding such a mold in a home does not mean that the mold poses a serious or extreme hazard to people in the home. There is very little known about the health significance of most household molds. If one has a specific mold allergy and needs to know if that particular mold is present, then testing may be helpful. General tests to determine total numbers of molds or spores in air samples may be useful in determining if there is a significant but unidentified indoor source of mold. There are private testing firms that offer such evaluations commercially. County and state agencies in Oregon do not have resources for inspecting private homes or testing them for mold.


What should I do if I have moldy conditions in my home?

Often rooms, closets or other spaces that are inadequately ventilated and/or heated, or articles stored in such areas will develop mold problems. The most important thing to do is to determine where the excessive moisture is coming from, and correct that problem. Molds cannot grow on dry materials even if all other conditions are ideal for mold growth. Conversely, mold and mildew cannot be controlled where moist materials exist. Growing colonies of mold can be killed by swabbing or spraying with a strong solution (11/2 cup per gallon of water) of household bleach. However, if the material remains moist, the mold will grow back very quickly. Once the material is dried and the mold has been killed, loose mold and damaged material should be removed with standard household cleaning materials. Washing with soap and water is frequently sufficient. Often repair of surfaces and refinishing is required. Damaged paper or fabrics such as carpets, rugs, drapes, stuffed furniture, bedding, and clothing may not be salvagable at all. Damp sheetrock and loose or spongy floor-covering may indicate that the interior of a wall or floor is wet or moist. This could indicate serious internal structural problems.

How can mold be safely removed?

When removing mold or handling moldy materials it is wise to avoid direct skin contact with the mold. Impervious gloves, long pants and long sleeves should be worn. It is best to handle moldy materials when they are damp. Materials that have been wet and moldy may have become dry but are still seriously contaminated with dead mold and mold spores. Such dry materials release many more spores and small particles into the air. If the materials are dusty, it is advisable to wear a fabric or paper dust mask over the nose to filter out dust particles. Make sure the area where you are working is well ventilated. Moldy materials should be tied tightly in plastic bags and placed in the garbage before they dry out.


What should I do if someone in my family has an illness thought to be caused be mold?

If you believe that you or anyone in your household is suffering from mold-related illness, it is important to seek medical attention. A physician can confirm irritant symptoms, can diagnose infection or determine if symptoms are indicative of allergy. Many of the symptoms caused by mold irritants and by mold allergies can also be caused by other agents commonly found in homes.


Is it likely that mold in my home is life-threatening?

No. Even though there are some molds that could produce life-threatening illness under the right growth and exposure conditions, serious mold-related illnesses caused by household mold exposure are very rare. Toxigenic molds such as Stachybotrys, Aspergillis, Penecillium and others are commonly found in homes, but rarely cause severe or life-threatening illness.


Who can I call for advice for Assistance?

If you are ill, contact your health care provider. For general information and advice you can call your county health department. If you are interested in commercial inspection or testing in your home you can firms listed under "Environmental Services", "Laboratories-Analytical" and "Industrial Hygiene" in your local telephone business listings.


To request a mold information packet (pdf)  you may contact Environmental Toxicology at 971-673-0440, e-mail us at   general.toxicology@state.or.us, or download our mold information packet (pdf).