Why is mold growing in my home?

Molds are part of the natural environment.  Outdoors, molds play a valuable part in nature by breaking down dead organic matter such as fallen leaves and dead trees, but indoors, mold growth should be avoided.  Molds reproduce by means of tiny spores; the spores are invisible to the naked eye and float through outdoor and indoor air.  Mold may begin growing indoors when mold spores land on surfaces that are wet.  There are many types of mold, and none of them will grow without water or moisture.

Can mold cause health problems?

Molds are usually not a problem indoors, unless mold spores land on a wet or damp spot and begin growing.  Molds have the potential to cause health problems.  Molds produce allergens (substances that can cause allergic reactions), irritants, and in some cases, potentially toxic substances (mycotoxins).  Inhaling or touching mold or mold spores may cause allergic reactions in sensitive individuals.  Allergic responses include hay fever-type symptoms, such as sneezing, runny nose, red eyes, and skin rash (dermatitis).  Allergic reactions to mold are common.  They can be immediate or delayed.  Molds can also cause asthma attacks in people with asthma who are allergic to mold.  In addition, mold exposure can irritate the eyes, skin, nose, throat, and lungs of both mold-allergic and non-allergic people.  Symptoms other than the allergic and irritant types are not commonly reported as a result of inhaling mold.  Research on mold and health effects is ongoing.  This brochure provides a brief overview; it does not describe all potential health effects related to mold exposure.  For more detailed information consult a health professional.  You may also wish to consult your state or local health department.

How do I get rid of mold?

Molds gradually destroy the things they grow on. You can prevent damage to your home and furnishings, save money, and avoid potential health problems by controlling moisture and eliminating mold growth.  It is impossible to get rid of all mold and mold spores indoors; some mold spores will be found floating through the air and in house dust.  The mold spores will not grow if moisture is not present.  Indoor mold growth can and should be prevented or controlled by controlling moisture indoors.  If there is mold growth in your home, you must clean up the mold and fix the moisture problem.  If you clean up the mold, but don't fix the moisture problem, then, most likely, the mold problem will come back.

Who and How to clean-up mold?

Who should do the cleanup depends on a number of factors.  One consideration is the size of the mold problem.  If the moldy area is less than about 10 square feet (less than roughly a 3 ft. by 3 ft. patch), in most cases, you can handle the job yourself, following the guidelines below.  However:

• If there has been a lot of water damage, and/or mold growth covers more than 10 square feet, consult EPA's Mold Remediation in Schools and Commercial Buildings.  Although focused on schools and commercial buildings, this document is applicable to other building types.
   

• If you choose to hire a contractor (or other professional service provider) to do the cleanup, make sure the contractor has experience cleaning up mold.  Check references and ask the contractor to follow the recommendations in EPA's Mold Remediation in Schools and Commercial Buildings, the guidelines of the American Conference of Governmental Industrial Hygenists (ACGIH), or other guidelines from professional or government organizations.
   

• If you suspect that the heating/ventilation/air conditioning (HVAC) system may be contaminated with mold (it is part of an identified moisture problem, for instance, or there is mold near the intake to the system), consult the EPA's guide Should You Have the Air Ducts in Your Home Cleaned? before taking further action.  Do not run the HVAC system if you know or suspect that it is contaminated with mold - it could spread mold throughout the building.
   

• If the water and/or mold damage was caused by sewage or other contaminated water, then call in a professional who has experience cleaning and fixing properties damaged by contaminated water.
   

• If you have health concerns, consult a health professional before starting cleanup.

Should I use bleach to clean up mold?

• The key to mold control is moisture control.

• Scrub mold off hard surfaces with detergent and water, and dry completely.

• Fix plumbing leaks and other water problems as soon as possible.  Dry all items completely.

• Absorbent or porous materials, such as ceiling tiles and carpet, may have to be thrown away if they become moldy.  Mold can grow on or fill in the empty spaces and crevices of porous materials, so the mold may be difficult or impossible to remove completely.
   

• Avoid exposing yourself or others to mold (see discussions: What to Wear When Cleaning Moldy Areas and Hidden Mold).
   

• Do not paint or caulk moldy surfaces.  Clean up the mold and dry the surfaces before painting.  Paint applied over moldy surfaces is likely to peel.
   

• If you are unsure about how to clean an item, or if the item is expensive or of sentimental value, you should consult a specialist.  Specialists in furniture repair, restoration, painting, art restoration and conservation, carpet and rug cleaning, water damage, and fire or water restoration are commonly listed in phone books or on the internet.  Be sure to ask for and check references.  Look for specialists who are affiliated with professional organizations.

What are ten things I need to know about mold?

1. Potential health effects and symptoms associated with mold exposures include allergic reactions, asthma, and other respiratory complaints.  

2. There is no practical way to eliminate all mold and mold spores in the indoor environment; the way to control indoor mold growth is to control moisture.

3. If mold is a problem in your home or school, you must clean up the mold and eliminate sources of moisture.

4. Fix the source of the water problem or leak to prevent mold growth.

5. Reduce indoor humidity (to 30-60% ) to decrease mold growth by: venting bathrooms, dryers, and other moisture-generating sources to the outside; using air conditioners and de-humidifiers; increasing ventilation; and using exhaust fans whenever cooking, dishwashing, and cleaning.

6. Clean and dry any damp or wet building materials and furnishings within 24-48 hours to prevent mold growth.

7. Clean mold off hard surfaces with water and detergent, and dry completely. Absorbent materials such as ceiling tiles, that are moldy, may need to be replaced.

8. Prevent condensation: Reduce the potential for condensation on cold surfaces (i.e., windows, piping, exterior walls, roof, or floors) by adding insulation.

9. In areas where there is a perpetual moisture problem, do not install carpeting (i.e., by drinking fountains, by classroom sinks, or on concrete floors with leaks or frequent condensation).

10. Molds can be found almost anywhere; they can grow on virtually any substance, providing moisture is present. There are molds that can grow on wood, paper, carpet, and foods.

Are there Federal regulations or standards regarding mold?

Standards or Threshold Limit Values (TLVs) for airborne concentrations of mold, or mold spores, have not been set. Currently, there are no EPA regulations or standards for airborne mold contaminants.

Should I have the air ducts in my home cleaned?

The EPA's guide Should You Have the Air Ducts in Your Home Cleaned? is instructive.  We have provided an excerpt on duct cleaning and mold from this guide which follows. Please review the entire document for additional information on duct cleaning and mold.

You should consider having the air ducts in your home cleaned if:

There is substantial visible mold growth inside hard surface (e.g., sheet metal) ducts or on other components of your heating and cooling system. There are several important points to understand concerning mold detection in heating and cooling systems:

• Many sections of your heating and cooling system may not be accessible for a visible inspection, so ask the service provider to show you any mold they say exists.

• You should be aware that although a substance may look like mold, a positive determination of whether it is mold or not can be made only by an expert and may require laboratory analysis for final confirmation.  For about $50, some microbiology laboratories can tell you whether a sample sent to them on a clear strip of sticky household tape is mold or simply a substance that resembles it.

• If you have insulated air ducts and the insulation gets wet or moldy it cannot be effectively cleaned and should be removed and replaced.

• If the conditions causing the mold growth in the first place are not corrected, mold growth will recur. 

(The above excerpt is from the EPA guide Should You Have the Air Ducts in Your Home Cleaned?)

What about Asthma and Mold?

Molds can trigger asthma episodes in sensitive individuals with asthma.  People with asthma should avoid contact with or exposure to molds.  Here are some links to more information on asthma and mold:

EPA's Asthma website - www.epa.gov/asthma 

EPA's Asthma Brochure  (PDF, 2 pp, 245KB About PDF)

EPA's Mold page from Asthma web site

• Allergy & Asthma Network/Mothers of Asthmatics (AAN/MA): (800) 878-4403; www.aanma.org

• American Academy of Allergy, Asthma & Immunology (AAAAI): www.aaaai.org

• American Lung Association: 1-800-LUNG-USA (1-800-586-4872); www.lungusa.org

• Asthma & Allergy Foundation of America: (800) 7ASTHMA; www.aafa.org

• National Institute of Allergy and Infectious Diseases: www.niaid.nih.gov

What about mold in large buildings?

The EPA has a number of resources available on this subject. We recommend that you can start with the Indoor Air Quality Building Evaluation and Assessment Model (I-BEAM).  I-BEAM updates and expands EPA's existing Building Air Quality guidance and is designed to be comprehensive state-of-the-art guidance for managing IAQ in commercial buildings.  This guidance was designed to be used by building professionals and others interested in indoor air quality in commercial buildings. I-BEAM contains text, animation/visual, and interactive/calculation components that can be used to perform a number of diverse tasks. See www.epa.gov/iaq/largebldgs/i-beam/index.html 

Is sampling/testing for mold necessary?

In most cases, if visible mold growth is present, sampling is unnecessary.  Since no EPA or other federal limits have been set for mold or mold spores, sampling cannot be used to check a building's compliance with federal mold standards.  Surface sampling may be useful to determine if an area has been adequately cleaned or remediated.  Sampling for mold should be conducted by professionals who have specific experience in designing mold sampling protocols, sampling methods, and interpreting results.  Sample analysis should follow analytical methods recommended by the American Industrial Hygiene Association (AIHA), the American Conference of Governmental Industrial Hygienists (ACGIH), or other professional organizations.

What are biological pollutants, how do they affect indoor air quality?

Biological contaminants include bacteria, molds, mildew, viruses, animal dander and cat saliva, house dust, mites, cockroaches, and pollen. There are many sources of these pollutants. Pollens originate from plants; viruses are transmitted by people and animals; bacteria are carried by people, animals, and soil and plant debris; and household pets are sources of saliva and animal dander. The protein in urine from rats and mice is a potent allergen. When it dries, it can become airborne. Contaminated central air handling systems can become breeding grounds for mold, mildew, and other sources of biological contaminants and can then distribute these contaminants through the home.

By controlling the relative humidity level in a home, the growth of some sources of biological contaminants can be minimized. A relative humidity of 30-50 percent is generally recommended for homes. Standing water, water-damaged materials, or wet surfaces also serve as a breeding ground for molds, mildews, bacteria, and insects. House dust mites, the source of one of the most powerful biological allergens, grow in damp, warm environments.

What causes mold to develop?

Mold requires nutrients, water, oxygen and favorable temperatures to grow. Nutrients for mold are present in dead organic material such as wood, paper or fabrics; mold can also derive nutrients from some synthetic products such as paints and adhesives. Mold requires moisture, although some mold species can obtain that moisture from moist air when the relative humidity is above 70 per cent. Many molds thrive at normal indoor temperatures; few if any molds are able to grow below 40 F or above 100 F. Outside this range molds may remain dormant or inactive; they may begin to grow again when the temperature is more favorable. Temperatures well above 100 F will kill mold and mold spores, but the exact temperature required to kill specific species is not well established.

How does mold get into a building?

Molds are decomposers of organic material such as wood, plants and animals. Mold and mold spores are found in high concentrations wherever there is dead matter such as a pile of leaves, manure or compost. Spores are small bundles of genetic material and chemicals (similar to seeds) that molds make under certain conditions. Mold spores enter buildings through the air or on people, animals and objects that are brought into the building.

Are there harmful and non-harmful molds?

There are only a few molds that can cause infection in healthy humans. Some molds cause infections only in people with compromised immune systems. The biggest health problem from exposure to mold is allergy and asthma in susceptible people. There are more than 100,000 types of mold. Good information has been developed for only a small number of these molds – at least in terms of their effects on human health. Most people tolerate exposure to moderate levels of many different molds without any apparent adverse health effects.

Some molds produce powerful chemicals called “mycotoxins” that can produce illness in animals and people. Scientific knowledge about the health effects of these toxins on humans is quite limited.

Does mold affect everyone the same way?

No. Some individuals have a genetic makeup that puts them at risk for developing allergies to mold. People who have an allergy to mold, especially if they also have asthma, can become ill from exposure to a small amount of mold. Individuals also seem to be quite different in their response to exposure to the toxic chemicals that some molds release. These differences between individuals contribute to the difficult question of determining safe exposure limits for mold.

How much mold exposure is harmful?

No one knows the answer to this question for several reasons. Individuals are very different with respect to the amount of mold exposure they can tolerate. Children under the age of one year may be more susceptible to the effects of some molds than older individuals. Measuring or estimating “exposure” levels is very difficult. “Exposure” means the amount of mold (microscopic spores and mold fragments) that gets into a person usually by breathing, but also by eating or absorption through the skin. For example, a building may have a lot of mold in the walls but very little of that mold is getting into the air stream. In that case the people working or living in that building would have little mold exposure.

Can mold exposure cause brain damage or death?

Although some “experts” claim that individuals have brain damage or have died because of exposure to mold and especially mold toxins, there is no good science at this time to support these claims. Consequently it is prudent to minimize one’s exposure to really moldy environments. By “really moldy” we mean where there are large visible areas of mold (more than a few square feet) or the building has a “musty” odor because of hidden mold growth. There are many epidemiological studies showing that people who live in houses with dampness have many more health problems, especially respiratory, than do people who live in dry houses. This association does not necessarily prove that it is the mold that is responsible for the increase in illness. However, it is does support the assertion that mold and damp areas should be remediated rather than increase health risks to persons living in damp and/or moldy buildings.

Does tighter building construction promote mold development?

Tighter building construction does not by itself promote mold growth, but tight construction combined with some poor choices in design, building materials or operations can increase the probability of mold growth. What do we mean? The tighter the building construction the less air exchange there is between the inside air and the outside air.  Whatever gets into the inside air stays there longer than it would in a house with loose construction. Moisture that gets into the air from activities such as cooking, bathing and even breathing will remain in a tight house longer than it would in a loose house. That’s why exhaust fans should be installed in bathrooms and kitchens and vented to the outside. Clothes dryers should also be vented to the outside.

Tight construction permits control of the air exchange between the inside and the outside and can prevent moisture in walls and roofs.  Controlling moisture, including indoor relative humidity is the key to preventing mold growth. Tight building construction when combined with source control of moisture (exhaust fans) and controlled ventilation (intentional introduction of outside air) reduces the probability of mold growth in a building.  Controlled ventilation can be provided by a duct that brings outside air to the return side of the air handler of a forced air system. A timing device or fan cycler can be programmed to have the air handler turn on for a specified number of minutes each hour even when there is no call for heating or cooling.  In cold climates, controlled ventilation is frequently provided by a heat recovery ventilator (HRV).

Do new building materials (e.g. drywall or paper-faced gypsum board) promote mold growth?

Mold needs water, a nutrient source, oxygen and a favorable temperature to grow. Many species of mold love paper-faced gypsum board. Why? Making paper involves the mechanical and chemical processing of wood. Paper is largely pre-digested so it is easy for mold to get nutrients from the paper. But unless there is enough moisture present mold can’t grow on the paper. If paper-faced gypsum board is kept dry, it can be used and still not have mold. This material is kept dry by controlling the interior relative humidity, keeping rain from entering roofs and walls, and NOT using paper-faced gypsum in areas that are likely to get wet. This means no paper-faced gypsum board in shower and tub areas. Cement board, mortar or non-paper-faced gypsum can safely be used in these damp areas because these products do not contain nutrients to support mold growth.

Are there reliable tests to indicate the presence of mold?

Almost all of us already have two effective mold detectors: our eyes and our noses. If black or green discoloration is noticed that is fuzzy in appearance and is in a location that is damp or has been damp, it is almost certainly mold. If a building smells musty, there probably is mold somewhere; the mold may be on boxes stored in a basement or in walls or in the crawl space. If you want to find mold, look for the presence of water or a location where water was likely to have been. If there is still any question about whether the black stuff is mold, have a reliable laboratory examine the material. All you need to know is whether mold is seen when the material is examined under the microscope.

An increasing number of companies are offering “air testing for mold.” On the surface this seems like a reasonable thing to do. The problem, however, is that the results of most air sampling for mold are meaningless for two reasons. Air sampling for mold was not developed to determine if an environment was safe or had a dangerous level of mold in the air. Air sampling was developed to help identify the location of a hidden reservoir of mold. If the source of mold is already identified, air sampling does not provide additional meaningful information. Furthermore, safe or toxic levels of airborne mold have not been established. An individual air sample for mold provides a “snapshot” of what was in the air during the few minutes of sampling. The results may not be indicative of the amount of mold that is in the air during most of the day.

Air sampling for mold should be done either to obtain an answer to a question that cannot be answered without the air sampling or to obtain data as part of a research project. The Center for Disease Control (CDC), the U.S. Environmental Protection Agency (EPA) and the American Conference of Governmental Industrial Hygienists do not recommend routine air testing for mold.

If mold is present, what’s the best way to get rid of it?

The answer depends on how much mold is present and where it is located. If the mold is on furnishings or boxes, simply discard the materials. Moldy materials are not considered hazardous waste; they can be sent to a regular landfill. However, it is smart to seal the mold material in heavy plastic to protect the people who handle it in transit and prevent spreading large amounts of the mold into the building as you carry the material out of it.

If the mold is on a hard surface but occupies less than 10 square feet wash the area with soapy water (scrubbing with a brush may be necessary), rinse and allow the area to dry before repainting. If you have asthma, severe allergies or a weakened immune system, have someone else to do the clean up.

Larger areas (greater than 10 square feet in area) should be cleaned by someone with experience in doing this type of work.  Remember, determine what caused the moisture problem and correct that problem.  Otherwise, mold is likely to recur.

Is it possible to completely eliminate mold from the inside of a home or office building?

The answer depends upon what is meant by “completely eliminate mold.” To keep a building completely free of mold spores requires very efficient air filtration and is only accomplished in special situations such as hospital operating rooms and manufacturing “clean rooms.” Remember, mold spores are in the outside air virtually all the time and some will always find their way inside buildings.

More importantly, it is absolutely possible to keep mold from growing inside a building. Moisture control is the key to controlling mold in interior spaces. Air filtration can contribute to lowering mold spores in the air but is secondary to moisture control.

We hope that this Question and Answer section has been helpful and informative.  Please call with any further questions you may have. 

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