A Brief Guide to Mold, Moisture and Your Home | US EPA (2023)
This Guide is also available as a downloadable pdf and en español
On this page:
Overview
Mold Basics
Mold Cleanup
Mold Cleanup Guidelines
What to Wear When Cleaning Moldy Areas
Is the Cleanup Complete?
Moisture and Mold Prevention and Control Tips
Hidden Mold
Cleanup and Biocides
Additional Resources
Overview
This Guide provides information and guidance for homeowners and renters on how to clean up residential mold problems and how to prevent mold growth. The content on these web pages is based on EPA's publication "A Brief Guide to Mold, Moisture and Your Home." Updates have been made to some resources and links.
Mold Basics
The key to mold control is moisture control.
If mold is a problem in your home, you should clean up the mold promptly and fix the water problem.
It is important to dry water-damaged areas and items within 24-48 hours to prevent mold growth.
Why is mold growing in my home?
Molds are part of the natural environment. Outdoors, molds play a 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).
Magnified mold spores
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
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 [guidance] 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?
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 water problem. If you clean up the mold, but don't fix the water problem, then, most likely, the mold problem will come back.
Mold Cleanup
If you already have a mold problem - act quickly. Mold damages what it grows on. The longer it grows, the more damage it can cause.
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, follow the guidelines. 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 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 buildings damaged by contaminated water.
If you have health concerns, consult a health professional before starting cleanup.
Mold Cleanup Guidelines
Bathroom Tip:
Places that are often or always damp can be hard to maintain completely free of mold. If there's some mold in the shower or elsewhere in the bathroom that seems to reappear, increasing ventilation (running a fan or opening a window) and cleaning more frequently will usually prevent mold from recurring, or at least keep the mold to a minimum.
Tips and techniques
The tips and techniques presented in this section will help you clean up your mold problem. Professional cleaners or remediators may use methods not covered in this publication. Please note that mold may cause staining and cosmetic damage. It may not be possible to clean an item so that its original appearance is restored.
Fix plumbing leaks and other water problems as soon as possible. Dry all items completely.
Scrub mold off hard surfaces with detergent and water, and dry 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 may wish to 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. Be sure to ask for and check references. Look for specialists who are affiliated with professional organizations.
What to Wear When Cleaning Moldy Areas
It is important to take precautions to limit your exposureto mold and mold spores.
Avoid breathing in mold or mold spores. In order to limit your exposure to airborne mold, you may want to wear an N-95 respirator, available at many hardware stores and from companies that advertise on the Internet. (They cost about $12 to $25.) Some N-95 respirators resemble a paper dust mask with a nozzle on the front, others are made primarily of plastic or rubber and have removable cartridges that trap most of the mold spores from entering. In order to be effective, the respirator or mask must fit properly, so carefully follow the instructions supplied with the respirator. Please note that the Occupational Safety and Health Administration (OSHA) requires that respirators fit properly (fit testing) when used in an occupational setting; consult OSHA for more information (800-321-OSHA or osha.gov).
Wear gloves. Long gloves that extend to the middle of the forearm are recommended. When working with water and a mild detergent, ordinary household rubber gloves may be used. If you are using a disinfectant, a biocide such as chlorine bleach, or a strong cleaning solution, you should select gloves made from natural rubber, neoprene, nitrile, polyurethaneor PVC (see Cleanup and Biocides). Avoid touching mold or moldy items with your bare hands.
Wear goggles. Goggles that do not have ventilation holes are recommended. Avoid getting mold or mold spores in your eyes.
How Do I Know When the Remediation or Cleanup is Finished?
You must have completely fixed the water or moisture problem before the cleanup or remediation can be considered finished.
You should have completed mold removal. Visible mold and moldy odors should not be present. Please note that mold may cause staining and cosmetic damage.
You should have revisited the site(s) shortly after cleanup and it should show no signs of water damage or mold growth.
People should have been able to occupy or re-occupy the area without health complaints or physical symptoms.
Ultimately, this is a judgment call; there is no easy answer. If you have concerns or questions consult our Frequently Asked Questions database and ask a question if you don't find what you need.
Moisture and Mold Prevention and Control Tips
Moisture Controlis theKeytoMold Control
When water leaks or spills occur indoors -act quickly. If wet or damp materials or areas are dried 24-48 hours after a leak or spill happens, in most cases mold will not grow.
Clean and repair roof gutters regularly.
Make sure the ground slopes away from the building foundation, so that water does not enter or collect around the foundation.
Keep air conditioning drip pans clean and the drain lines unobstructed and flowing properly.
Keep indoor humidity low. If possible, keep indoor humidity below 60 percent (ideally between 30 and 50 percent) relative humidity. Relative humidity can be measured with a moisture or humidity meter, a small, inexpensive ($10-$50) instrument available at many hardware stores.
If you see condensation or moisture collecting on windows, walls or pipesact quicklyto dry the wet surface and reduce the moisture/water source. Condensation can be a sign of high humidity.
Actions that will help to reduce humidity
Vent appliances that produce moisture, such as clothes dryers, stoves, and kerosene heaters to the outside where possible. (Combustion appliances such as stoves and kerosene heaters produce water vapor and will increase the humidity unless vented to the outside.)
Use air conditioners and/or de-humidifiers when needed.
Run the bathroom fan or open the window when showering. Use exhaust fans or open windows whenever cooking, running the dishwasher or dishwashing, etc.
Actions that will help prevent condensation:
Reduce the humidity (see preceding page)
Increase ventilation or air movement by opening doors and/or windows, when practical. Use fans as needed.
Cover cold surfaces, such as cold water pipes, with insulation.
Increase air temperature.
Renters:Report all plumbing leaks and moisture problems immediately to your building owner, manager, or superintendent. In cases where persistent water problems are not addressed, you may want to contact local, state, or federal health or housing authorities. You can also contact your state health department.
Test or Sampling for Mold
Is sampling for mold needed? 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.
Hidden Mold
Suspicion of hidden mold
You may suspect hidden mold if a building smells moldy, but you cannot see the source, or if you know there has been water damage and residents are reporting health problems. Mold may be hidden in places such as the back side of dry wall, wallpaper, or paneling, the top side of ceiling tiles, the underside of carpets and pads, etc. Other possible locations of hidden mold include areas inside walls around pipes (with leaking or condensing pipes), the surface of walls behind furniture (where condensation forms), inside ductwork, and in roof materials above ceiling tiles (due to roof leaks or insufficient insulation).
Investigating hidden mold problems
Investigating hidden mold problems may be difficult and will require caution when the investigation involves disturbing potential sites of mold growth. For example, removal of wallpaper can lead to a massive release of spores if there is mold growing on the underside of the paper. If you believe that you may have a hidden mold problem, consider hiring an experienced professional.
Cleanup and Biocides
Biocides are substances that can destroy living organisms. The use of a chemical or biocide that kills organisms such as mold (chlorine bleach, for example) is not recommended as a routine practice during mold cleanup. There may be instances, however, when professional judgment may indicate its use (for example, when immune-compromised individuals are present).
In most cases, it is not possible or desirable to sterilize an area; a background level of mold spores will remain - these spores will not grow if the moisture problem has been resolved. If you choose to use disinfectants or biocides, always ventilate the area and exhaust the air to the outdoors. Never mix chlorine bleach solution with other cleaning solutions or detergents that contain ammonia because toxic fumes could be produced.
Please note:Dead mold may still cause allergic reactions in some people, so it is not enough to simply kill the mold, it must also be removed.
Additional Resources
Acknowledgements
EPA would like to thank Paul Ellringer, PE, CIH, for providing the photo ofMold growing on the back side of wallpaper.
Notes
Please note that this document presents recommendations. EPA does not regulate mold or mold spores in indoor air
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.
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.
Sometimes, humidity or dampness (water vapor) in the air can supply enough moisture for mold growth. Indoor relative humidity (RH) should be kept below 60 percent -- ideally between 30 percent and 50 percent, if possible. Low humidity may also discourage pests (such as cockroaches) and dust mites.
– Scrub the entire moldy area with a non-ammonia soap or detergent, or a commercial cleaner, in hot water, using sponges or rags, until all mold is gone. – Use a stiff brush or cleaning pad on cement-block walls and other uneven surfaces. – Rinse cleaned items with water and dry thoroughly.
Keep the thermostat at 78 degrees or above. A higher thermostat setting and slightly warmer air temperature results in drier indoor air. In the cooling mode, temperatures lower than 78 degrees generate more humid air and cool indoor surfaces, increasing condensation that breeds mold.
Aspergillus – This genus of mold grows worldwide and is one of the most commonly occurring molds in hospitals. Its spores can trigger an allergic reaction in some people. Aspergillus is so abundant that it is probably impossible to avoid breathing in at least some of its spores.
What is healthy humidity? Most people find that a relative humidity between 30 to 60 percent is the most comfortable, with indoor humidity ideally between 30 to 50 percent.
Keep indoor humidity between 30 and 50 percent. Use a moisture or humidity gauge, available at most hardware stores, to see if the humidity in your home is at a good level. To increase humidity, use a vaporizer or humidifier. To decrease humidity, open the windows if it is not humid outdoors.
Research shows that the ideal relative humidity for your home is between 40%-60%. However, to discourage the growth and spread of mold, levels should be kept below 50%.
Bleach kills virtually every species of indoor mold that it comes into contact with including mold spores which leaves a sanitized surface making it resistant to future mold growth.
Hydrogen peroxide kills mold spore on contact by breaking down proteins and DNA. It's normally used to clean mold on porous and non-porous surfaces. Ionized hydrogen peroxide can kill mold spores in the air, but it requires the use of a special fogging machine.
Use undiluted white vinegar on hard surfaces in kitchens and baths. A bleach solution also works to kill mold. Mix one cup of bleach in a gallon of water, apply to the surface and don't rinse. Mix a 50/50 solution of ammonia and water.
It is also very important that there is adequate ventilation in the room. Open a window or door so the mold spores can escape, instead of staying locked in your home.
Your air conditioner is designed to help dehumidify your home, removing excess moisture and preventing mold's growth. So keeping your air conditioner running in humid weather and situations is a proactive step to take. Mold also likes stale air.
Leaving the AC off for long periods of time gives mold and bugs enough time to settle in the higher humidity. To prevent this, raise the temperature on your AC unit 7 to 10 degrees and leave it running while you're away.
Some people are sensitive to molds. For these people, exposure to molds can lead to symptoms such as stuffy nose, wheezing, and red or itchy eyes, or skin. Some people, such as those with allergies to molds or with asthma, may have more intense reactions.
These symptoms usually first appear 2 to 9 hours after exposure and last for 1 to 3 days. Other affected persons have progressive shortness of breath and cough, as well as weight loss.
Mildew refers to certain kinds of mold or fungus. The term mildew is often used generically to refer to mold growth, usually with a flat growth habit. Molds include all species of microscopic fungi that grow in the form of multicellular filaments, called hyphae.
Generally speaking, a concentration of mold spores below 500 sp/m3 is considered normal. A concentration of mold spores above 500 sp/m3 is considered high. Therefore, if your report comes up with high concentrations of mold, it will likely advise you to remediate the problem.
The Most Dangerous Molds. Toxic molds fall into five categories. Those categories are Penicilium, Fusarium, Stachybotrys, Aspergillus and Cladosporium.
Black mold is a dark colored mold that tends to be more slimy and wet than many other molds. It grows in small clusters making it look like dots. Often there is visible water damage near visible mold. You will also notice a musty smell nearby.
Every home is different, but a level between 30 and 40 per cent humidity is typically ideal for keeping your home warm and comfortable in the winter, without leaving condensation on the windows. In the summer, that level can be higher, between 50 and 60 per cent.
Comfortable levels of humidity range between 30% and 60%, however, the ideal humidity level, according to ASHRAE, is between 45% and 55%. Anything above 55% is considered to be high.
The optimal relative humidity level is between 30 and 50 percent, according to Energy Star (and 30 to 40 percent in colder areas during heating season). If the humidity is higher than that, it can breed dust mites, mildew, and mold, and trigger allergies.
What are the ideal humidity levels I should consider in my home? Building and government housing agencies recommend that homeowners keep humidity levels between 20% and 50%. The warmer the air in your home the more water it can hold.
The best relative humidity for sleeping and other indoor activities has been debated. According to the Environmental Protection Agency, the best indoor relative humidity falls between 30% and 50%, and it should never exceed 60%. Other studies suggest 40% to 60% is a better range.
When the indoor humidity level is below 30 percent, the air is too dry, which can harm both a home's structural integrity and the homeowners' health. Conversely, when the level is above 60 percent, the air is too wet, which is also harmful to both the home and the homeowners.
Research from the Building Science Corporation found that humidity of 70% or higher adjacent to a surface can cause serious damage to the property. The Health and Safety Executive recommends that relative humidity indoors should be maintained at 40-70%, while other experts recommend that the range should be 30-60%.
Chlorine bleach is the most effective home-removal product for killing mold spores. However, if the infestation is small, you can use distilled white vinegar or hydrogen peroxide to kill the spores.
Prepare equal part lemon juice and vinegar and a lesser quantity of baking soda. Mix all the ingredients to form a thick paste. Then with the aid of cloth or brush, apply on the moldy areas and scrub. Leave the paste on the mold for about five minutes before washing with clean water.
In such cases, a solution of diluted bleach provides the fastest way to kill mold on walls or flooring. Prepare the solution by adding one cup of bleach into a bucket that contains about a gallon of warm water. Then proceed to scrub the mold vigorously with a stiff-bristled brush you've dipped in the bleach solution.
White vinegar is a mildly acidic product that cleans, deodorizes, and disinfects. It can also kill 82% of mold species, including black mold, on porous and non-porous surfaces. You can use it safely on most surfaces, and its offensive odor goes away quickly. Pour undiluted white vinegar into a spray bottle.
Mould will easily grow and spread if the right conditions are present. So, dehumidifiers don't kill mould, but they can help to prevent it from growing inside your home by reducing humidity. However, the best way to deal with it is to get rid of its source.
Termites. Mold releases mycotoxins into the air—these draw termites to the area. As the damp conditions cause wood to rot and deteriorate, it becomes easier for termites to penetrate the wood and eat away at it.
Mold hates light. Other than moisture there's nothing mold loves more than dark places. An easy prevention against mold growth is opening your blinds and shades. If it's warm enough out, open the windows.
While it is possible to use bleach to kill mold as well, experts agree that vinegar is a much better option. Unlike bleach, vinegar can effectively kill the mold at the root, which means it's less likely to return. Vinegar is also less toxic than bleach, making it a better choice for household use.
If the mold is still hanging on, it's time to bring out the borax, which is an alkaline mineral salt cleaner that's safer to use than bleach. Combine a tablespoon of borax with a cup of water, then apply this solution to the mold with a soft-bristled brush.
Many fungi grow well at temperatures between 60 and 80 degrees Fahrenheit, which are also ideal temperatures for human comfort. In addition, as mentioned above, temperature gradients often produce the moisture needed for mold growth.
Airtight windows and buildings require more active ventilation. your kitchen and bathroom has an extractor fan. This will help prevent moisture reaching other rooms, especially bedrooms, which are often colder and more likely to get condensation. Do not block air-brick vents or ventilators.
Do Humidifiers Get Rid Of Mold? Unfortunately, humidifiers will not get rid of mold. Instead, they may add to a current mold problem or can even cause one. Also, since mold needs moisture to grow, you can even find mold growing inside humidifier units.
Combatting mold growth during the summer can be as easy as turning on your A/C. Simply using your air conditioner to keep your home's temperature between 68 and 74 degrees and keeping humidity levels between 30-60% prevents the growth of mold.
The ideal temperature is between 77 and 86 degrees Fahrenheit. During the summer months, temperatures are often higher than normal inside the home. Make an effort to keep temperatures inside the home lower during the summer months. Setting the thermostat to the low 70s makes it more difficult for mold to grow.
Mold Growth- The colder you keep your home, the colder the walls, ceiling, floors, windows and more will be. Water vapor that gets into these porous materials is the ideal place for mold to grow. This also can happen when humid outdoor air gets into the home and the indoor humidity is low in the air.
The answer to the question “is it cheaper to leave your air conditioner on all day?” is a resounding yes. You'll save money on your energy and repair bills, especially during the summer months.
The Facts. Leaving your air conditioner on is actually more efficient than frequently turning it on and off. Having your AC on also allows you to better control humidity in your home throughout the day. The lower the humidity in a home, the more comfortable it feels during hot weather.
EPA set a Maximum Contaminant Level Goal (MCLG) for each contaminant. The MCLG is the maximum level of a contaminant in drinking water at which no known or anticipated adverse effect on the health of persons would occur, and which allows an adequate margin of safety. MCLGs are not enforceable.
Definition: EPA-defined standard conditions of temperature and pressure are 68°F (20°C) and 14.7 psia (760 mm Hg). Definition: Standard cubic feet per minute is the gas flow rate at standard conditions expressed in the American Engineering system of units.
200-500 spores – the most common species (Penicillium/Aspergillus, Cladosporium and Curvularia) are typically not an issue and stay within the normal range. 500-1500 spores – sometimes the Penicillium/Aspergillus & Cladosporium levels are in this range and do not require remediation.
Water quality standards (WQS) are provisions of state, territorial, authorized tribal or federal law approved by EPA that describe the desired condition of a water body and the means by which that condition will be protected or achieved.
The Clean Air Act requires EPA to set National Ambient Air Quality Standards (NAAQS) NAAQS are currently set for carbon monoxide, lead, ground-level ozone, nitrogen dioxide, particulate matter, and sulfur dioxide. for six common air pollutants (also known as " criteria air pollutants.
The US federal primary drinking water standard maximum contaminant level (MCL) and the maximum contaminant level goal (MCLG) for nitrite (measured as nitrogen) are both set at 1 mg/L. The MCL was established to protect infants (below 6 months of age). The MCL and MCLG for nitrates are 10 mg/L each.
The fifth Unregulated Contaminant Monitoring Rule (UCMR 5) was published on December 27, 2021. UCMR 5 requires sample collection for 30 chemical contaminants between 2023 and 2025 using analytical methods developed by EPA and consensus organizations.
If all of a constituent in the sample completely dissolved or leached into the extraction fluid during the tumbling cycle, then the concentration of the constituent in the extraction fluid will always be 20 times less than its original con- centration in the sample, because it is diluted to 1/20th of its original ...
Some people are sensitive to molds. For these people, exposure to molds can lead to symptoms such as stuffy nose, wheezing, and red or itchy eyes, or skin. Some people, such as those with allergies to molds or with asthma, may have more intense reactions.
The most common types of mold include aspergillus, cladosporium and stachybotrys chartarum (also known as black mold). Aspergillus is a fairly allergenic mold that is commonly found on foods and in-home air-conditioning systems.
Spores of Aspergillus and Penicillium are rounded or slightly elongated, and smooth or ornamented depending on the species. Since these spores have no other distinguishing characteristics, laboratories usually lump them together as Aspergillus/Penicillium when they analyze air by direct microscopy (total spore counts).
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