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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 healthcare 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

  • Can I request the Air Quality Section (AQS) within the California Department of Public Health to inspect my home, enforce the housing code, or remediate my building?
    AQS does not conduct site visits or inspections, enforce housing codes, or perform water damage restoration. Inspections and code enforcement are handled by local code enforcement agencies (see next question).  
  • My landlord/property manager will not adequately address mold or dampness problems in my home. What are my rights as a tenant? Which agency should I contact for assistance?
    In California, landlords must provide a unit that is fit for occupation. The California Housing Code, as of January 1, 2016, says that if the amount of dampness or visible mold (or certain other conditions) in a dwelling is a danger to the health of occupants, the dwelling is substandard and the owner must remediate. If you suspect mold in your home, you can contact your local code enforcement agency and ask them to inspect for a violation of the housing code. If the local code inspector finds a violation and cites the unit as substandard housing, they can require the landlord to fix the violation. Identifying the appropriate local code enforcement agency may be difficult because code enforcement authority lies in different departments across different counties and cities. 
  • I have mold in my rental dwelling, and I know that mold is listed as a substandard condition in the State Housing Code. However, no local agency, city or county, will enforce this provision and make the owner fix the mold problem. Who can help me? 

    The State Housing Law, California Health and Safety Code (HSC), section 17920.3(a)(13), establishes that visible mold growth, as determined by health or code enforcement officers, would deem a residential building to be substandard. 

    Residents experiencing substandard conditions in residential buildings/dwellings, including the presence of mold in rental housing, are encouraged to contact their local health or code enforcement departments to determine the local agency with jurisdiction. HSC, sections 17960 and 17961, mandate that the building department and health departments/environmental agencies, respectively, of every city/county are responsible for enforcement of State Housing Law, State Housing Law Regulations, and the California Building Standards Code. Failure of the responsible local agencies to enforce the HSC sections referenced above, is a violation of State Law.

    NOTE: For information on additional local actions or proceedings, see HSC, division 13, part 1.5, chapter 5, article 3.

  • My neighbor’s mold is affecting me - what can I do?
    If appeals to the owner of the neighboring home are ineffective, you can try reaching out to your local code enforcement agency and explain your situation. The inspector may be able to determine if the neighboring structure does not meet housing standards.    

Testing for mold

  • Do I need to test for mold and identify the mold species in my home/building?
    • If you know you have a dampness or mold problem because you can see it (mold, water damage, or moisture) or smell it (moldy or musty odor):
      • You do not need to measure the amount or identify the type of mold.
      • Testing does not give you any more useful information.
    • Most importantly, measuring molds does not tell you if there is a health problem.
      • Mold tests typically count visible or cultured mold spores in the indoor air or on indoor surfaces—for example, Penicillium, Aspergillus, or Stachybotrys species.
      • There are no recommended “unhealthy levels” for spore concentrations or for particular kinds of molds.
    • If you want professional help, experienced building investigators can assess your home/ building for moisture or mold.
    • A building investigator’s conclusions from mold tests about water damage or mold growth are based only on their judgement, and not on solid scientific evidence. For example, some say that indoor mold levels higher than outdoor levels show that you have indoor mold growth, but this has not been scientifically proven, and mold levels vary widely over time both indoors and outdoors.
  • I have already tested for mold and have mold test results what do they mean?
    The inspector or laboratory that conducted the tests should provide you with their interpretation of the findings. However, we urge you to be cautious when considering these conclusions, because it is not clear that mold test results actually say anything about health risks, whatever the inspector or lab might say. If you know you have a dampness/mold problem because you can see it or smell it, you do not need further information from mold tests (see questions above and below).
  • Can I test for mold myself without hiring a professional?
    Surface and air sampling kits are commercially available, but we do not recommend their use. If you see or smell moisture/mold, mold testing does not provide further useful health information. Rather, you (or an expert) need to locate the moisture source and fix the underlying cause of the problem.
  • How do I find someone to inspect my home and locate the source of the mold or moisture problem?
    An experienced mold and moisture inspector is trained to identify the source of the mold or moisture problems, generally without measuring mold levels. There are no California regulations for mold inspectors. We cannot recommend any company in particular. Mold consultants can be found through professional associations such as the Indoor Air Quality Association (IAQA) and American Industrial Hygiene Association (AIHA). Mold inspectors may also be found through the National Organization of Remediators and Mold Inspectors (NORMI) and the National Association of Mold Remediators and Inspectors (NAMRI). These organizations are listed here strictly for informational purposes and listing them does not imply CDPH endorsement.
  • How do I identify a licensed contractor or experienced professional who can fix the mold and moisture problems in my home?
    Some licensed contractors have expertise in dealing with mold and moisture problems. There are no California regulations for licensing mold remediators. Mold remediators can be certified by national organizations such as 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. The California State Licensing Board (CSLB) has information on currently licensed contractors in the state.


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.


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