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Indoor Air Quality (IAQ) Section

Mold and Dampness 

Additional information on mold and dampness

Background: About Mold and Dampness

Health Effects of Mold

Brief History of Mold Regulation in California

Renters with Damp or Moldy Dwellings - Getting help​

Additional Resources with More Links

Molds are simple, microscopic organisms, present virtually everywhere, indoors and outdoors. Molds, along with mushrooms and yeasts, are fungi and are needed to break down dead plant and animal material and to recycle nutrients in the environment. Because molds grow by digesting organic material, they gradually destroy whatever they grow on. Molds can grow on surfaces or objects in buildings. Mold growth on surfaces can often be seen in the form of discoloration: frequently white, gray, brown, or black but also green and other colors. They may be visible or, if inside walls or building structures, not visible to you.
For molds to grow and reproduce, they need only a food source—any organic matter, such as leaves, wood,  paper, or dust—and moisture, which does not have to be liquid water but can be just a damp material or surface. Because organic matter is always available, moisture or dampness in buildings is thus the limiting factor determining whether mold can grow. Molds can usually grow whenever enough moisture is available.
Common sources of moisture that may lead to indoor mold problems include:

  • Flooding
  • Leaky roof
  • Sprinkler spray hitting a building
  • Plumbing leaks
  • Overflow from sinks or sewers
  • Damp basement or crawl space
  • Steam from showers or cooking
  • Humidifiers
  • Wet clothes hung to dry indoors
  • A clothes dryer that exhausts air indoors

Prevention is important to avoid mold problems. Inspect your home, school, or workplace regularly for signs and sources of indoor moisture and mold.

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Molds release tiny spores and even smaller particles that travel through the air. Everyone inhales some mold every day without apparent harm; however, molds can cause allergy, irritation or inflammation, or rarely, infection. Allergic reactions are the most well-recognized responses to inhaling mold spores, and some people are more sensitive to the effects of dampness mold.  However, it is becoming increasingly clear that individuals not sensitized to mold may experience health effects.

We know that dampness and mold cause health effects both in allergic and non-allergic people. If you can see mold, water damage, or moisture, or smell mold, there is at least some increased health risk. The more extensive or severe the dampness and mold, the greater the risk of health effects. We do not know whether specific types of mold are responsible, or whether bacteria or chemical emissions related to dampness also cause some of the health problems. The health effects consistently associated with indoor dampness and molds include:
  • Causation of new asthma
  • Asthma attacks in those who already have asthma
  • Allergic rhinitis (sneezing, congested nose, or runny nose)
  • Upper respiratory symptoms, such as stuffy or congested nose or sinuses, sore throat, or irritated nose or throat
  • Lower respiratory symptoms, such as wheezing, difficulty breathing, shortness of breath, or cough
  • Respiratory infections such as acute bronchitis
  • Eye irritation (burning, watery, or reddened eyes)
  • Eczema and skin rashes or irritation

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The 2001 Toxic Mold Protection Act (PDF; SB 732, Ortiz) directed the California Department of Health Services (now Department of Public Health or CDPH) to determine the feasibility of establishing health-based permissible exposure limits (PELS) for indoor mold. If that were possible, the CDPH was also directed to create programs to develop guidelines for mold assessment, clean-up, and disclosure in residences. However, CDPH responded in 2005 ("Report to the California Legislature on Implementation of the Toxic Mold Protection Act of 2001" PDF) that available evidence did not support the establishment of science-based PELs for indoor molds at that time. This view remains the CDPH position to date. Nevertheless, CDPH also stated that it "agrees with other building and health professionals that indoor dampness, water intrusion, or fungal growth should always be eliminated in a safe and efficient manner." This advice was expanded in the CDPH Statement on Indoor Dampness and Mold (PDF; revised 2016), based on the increased availability scientific information.

Dampness in your home living spaces has long been listed as a condition making a home substandard to a code inspector.  As of January 1, 2016, mold is also a condition that makes a home substandard in California. The owner of a rental property cited as substandard by a local (city or county) code inspector is required to repair the substandard condition. Below are the parts of the California Residential Building Code that refer to dampness and mold.

Any building or portion thereof including any dwelling unit, guestroom or suite of rooms, or the premises on which the same is located, in which there exists any of the following listed conditions to an extent that endangers the life, limb, health, property, safety, or welfare of the public or the occupants thereof shall be deemed and hereby is declared to be a substandard building:

(11) Dampness of habitable rooms.

(13) Visible mold growth, as determined by a health officer or a code enforcement officer, as defined in Section 829.5 of the Penal Code, excluding the presence of mold that is minor and found on surfaces that can accumulate moisture as part of their properly functioning and intended use.


The 2001 Toxic Mold Protection Act also directed the production of a consumer-oriented booklet that residential property owners will give to prospective tenants. We have developed a draft booklet for this purpose, and are posting it here for an open comment period.

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Visible mold is covered by the California Housing Code: visible residential mold at a level that may be hazardous to occupants is a condition that makes housing substandard. The visible mold can be cited by local code enforcement so that the owner is required to remediate the problem. Often the challenge for the renter, when the owner is unresponsive to requests to fix the problem, is to identify the proper code enforcement authority to enforce the California Housing Code. Note that our small group at CDPH does not do enforcement or inspections, but provides information to the public and does research to assist protection of the public.

Please refer to this Code Enforcement table for California counties and cities to look for information on whom to contact to get help with enforcing the housing code depending on where you reside.

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