Skip Navigation LinksFrequently-Asked-Questions-about-Mold

air quality section (AQS)

Frequently Asked Questions about Mold


General Health

  • What is mold and why is it growing indoors?
    Mold (and mildew) are common terms for fungi that can grow in damp locations in buildings, although molds are present everywhere, indoors and outdoors. Molds are important microorganisms because they help break down dead plant and animal material and recycle nutrients in the environment. There are many kinds of molds, and mold growth can have many forms and colors. To grow and reproduce, mold only needs food — any organic matter, such as leaves, wood, paper, or even dust — and moisture. Organic matter is almost always available, so whether mold grows depends mostly on whether there is moisture. By fixing moisture problems, you can keep mold from growing in your home.
  • What are the health effects of mold?
    The presence of visible mold, visible moisture, water-damaged materials, or mold odor in a building is clearly linked to increased risk of various respiratory health effects. These health effects include asthma development, asthma exacerbation, allergies, respiratory infections, and a variety of upper and lower respiratory symptoms. The more extensive or severe the dampness and mold, the greater the risk of health effects. The health effects also depend on the susceptibility of the occupants. Speak to your doctor if you have concerns about the health effects of mold.
  • Can a doctor tell me if the mold in my building is making me sick?            
    A doctor can test for and diagnose a small number of mold allergies. However, a person may have mold allergies for which there is no test. Also, molds can have health effects other than allergic reactions and can affect people who are not allergic. Still, it is a good idea to discuss your concerns with your healtcare provider.
  • Do I need to know if the mold in my building is "toxic mold" or "black mold"?
    No. Any type of mold that you see or smell in your building is a risk to your health and should be fixed. The more mold or moisture that you see or smell, the greater the risk to your health. There is currently no evidence that the particular kind of mold in your building matters.


Mold and dampness in my home

  • How do I know if I have a mold or moisture problem?
    Mold or moisture problems may be visible or hidden. Visible areas could include surfaces in the building itself and items in the building. Examples of hidden problem areas include beneath wallpaper, behind furniture, behind baseboards, or inside walls, floors, or ceilings. Signs of a mold or moisture problem in your home are:
    • Water-stained, discolored, or moldy surfaces
    • Water damage, such as warped floors, peeling or bubbled paint, or rotting wood
    • Damp surfaces, including condensation on windows or walls
    • An earthy, musty, or moldy smell
    You might also have a mold problem if people who are sensitive or allergic to mold have symptoms when they are in your home.
  • What are the main steps to fixing a mold or dampness problem?
    There are several steps to fixing a mold or dampness problem.
    • Find the damp or moldy areas
    • Fix the source of the moisture problems
    • Dry or replace wet materials
    • Clean or remove moldy materials

    Further information can be found on our Factsheet "Mold or Moisture in My Home: What Do I Do?" (PDF). 

  • What are the most common sources of excess moisture?
     Excess moisture can come from either indoor or outdoor sources. Indoor sources include:
    • Leaking or burst pipes
    • Insufficient venting where water is used (for example, bathrooms, laundry areas, and kitchens)
    • Condensation on cold surfaces
    Outdoor sources include:
    • Water intrusion (leaky roofs, leaky windows) and flooding
    • Outdoor surfaces that slope and drain water toward the home
    • Sprinklers and downspouts directing water at the house
  • I smell mold, but I don't see any — How do I find the mold or moisture problem?
    You are right not to ignore mold odor, because this is one of the best indicators of potential health risks from dampness or mold. If you cannot find the mold or moisture problem, you may need a general contractor experienced with water damage assessment to find the source of the mold odor. Thorough mold investigations may require some damage to building materials to find mold or dampness in hidden spaces. We do not recommend testing for mold [see section on Testing for Mold].
  • What materials can I effectively clean of mold and what should I remove?
    Generally, materials are either porous or non-porous. Non-porous materials (such as glass, plastic, metal, or ceramics) do not absorb water and can be effectively cleaned of mold [see next question]. Porous materials (such as drywall, ceiling tiles, drapes, or upholstered furniture) do absorb water and usually cannot be effectively cleaned of mold. If the porous materials look or smell moldy, they should be removed. In addition, porous materials that have stayed wet for more than a day or two may need to be removed, even if they do not yet look or smell moldy, because mold may have started to grow under some conditions.
  • How do I safely deal with moldy materials?
    If you are sensitive to mold or if the amount of mold is large, consider having another person or professional do the work. Use personal protective equipment, such as goggles, gloves, and an N-95 particulate respirator. A "dust mask" will not protect you from mold. It is also advisable to wear removable protective clothing (such as disposable suits) while handling moldy material, as mold can collect on clothes and be released later. It is important to prevent contamination from spreading from the source area to other areas in the home [see guidelines below]. It is also a good idea to ventilate the area you are cleaning to the outdoors during and after the work.

    Cleaning non-porous materials:
    Scrub non-porous materials thoroughly with soap and water to remove mold. We do not recommend using bleach or products that contain bleach. Bleach can be a respiratory hazard and disinfection is not necessary if you have cleaned the material thoroughly with soap.

    Removing porous materials:
    Moldy materials should be sealed in disposable bags or wrapped in plastic and disposed of as normal trash. The moldy material does not need to be treated as hazardous waste.
    The US EPA offers further tips and techniques for cleaning up mold in homes.
  • What methods are not effective for fixing dampness or mold problems?
    Painting over mold, even after applying a biocide, will not fix mold and dampness problems. Removing damaged materials, but not addressing the underlying moisture problem, is also ineffective. Running particle-removing air filters or air cleaners will not solve a mold problem.
  • How do I minimize risk to other home occupants during mold removal or remediation?
    Removing moldy materials can raise mold levels in the air, so it’s advisable for unprotected persons to avoid exposures during remediation. During and after remediation, precautions should be taken to prevent mold spores from contaminating other areas on the home. Containment of the remediation area and the moldy materials, including sealing vents to heating/air conditioning/ventilation systems, followed by cleanup are important safety measures. In larger remediation projects, containment may require sheeting and maintaining negative pressure in the containment area.
  • How do I know if the remediation was good enough and solved the problem?
    The best known indicator that the dampness-related health risks have been reduced is if the source of the moisture is remedied, all damaged materials have been cleaned or removed appropriately, and all remaining materials are dry and free of visible mold and mold odor. As of now, no mold tests or measurements can show when remediation efforts have been successful.
  • How do I prevent mold from growing again?
    Correcting the moisture problems and preventing or quickly responding to future moisture problems will keep mold from growing indoors. Also, porous materials that were previously moldy but not removed will be even more susceptible to mold regrowth.


Getting help with fixing a mold or dampness problem


Testing for mold



Mold and dampness in schools and workplaces


Standards and licensing for mold or dampness in California

  • What regulations about mold and moisture are there in California?
    Currently, there are limited regulations regarding mold and moisture in California.
    • The California housing code lists both mold and dampness as conditions of substandard housing that the owner must remediate if cited by a code enforcer.  
    • Regulations on moisture and mold in the workplace are enforced by Cal/OSHA.
    The following areas are not currently regulated
    • Science-based exposure limits for indoor molds cannot be established at this time, and none exist in California [see our "Brief History of Mold Regulation in California"].
    • There is no legal requirement in California for training, licensing, or certification of mold assessors to identify a mold or dampness problem or of mold remediators to fix a mold or dampness problem. Some other states, such as Louisiana, Texas, and New York, do require mold assessors or remediators be licensed in the state, but there are no federal licensing regulations.
  • Is a license required to be a mold inspector or remediator in California?
    At present, California has no state regulations about mold inspection, assessment, or remediation. Any business is subject to local requirements, such as for a business license. A company performing building construction or improvement valued at $500 or more (labor and materials costs) must have a state contractors’ license.
  • Could you direct me to information about obtaining a license or certification for inspecting or remediating mold?
    Several professional associations and commercial organizations offer training dealing with mold and dampness. Environmental health specialists and industrial hygienists are trained in contaminant sampling and building assessment, though not necessarily on mold-related issues. Pest control operators (PCOs) are trained in the assessment and treatment of buildings for wood-destroying organisms, including fungi. PCOs are licensed by the state, but receive no specific training on indoor mold issues. There are numerous commercial organizations that provide training for mold contractors, including the National Organization of Remediators and Mold Inspectors (NORMI), National Association of Mold Remediators and Inspectors (NAMRI), and Institute of Inspection, Cleaning, and Restoration (IICRC). These organizations are listed here strictly for informational purposes and listing them does not imply CDPH endorsement.


Page Last Updated :