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Mold and Dampness

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. Molds can grow on surfaces or objects in buildings. 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, or paper—and moisture. Because molds grow by digesting organic material, they gradually destroy whatever they grow on. 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.

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 the signs and sources of indoor moisture and mold.

Health Effects of Mold

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 inflammation, allergy, or infection. Allergic reactions are the most well-recognized responses to inhaling mold spores.

While we know there are health effects associated with indoor dampness and mold, we do not know how much specific molds are responsible, and how much of the effects might be caused by bacteria or chemical emissions. We know that dampness and mold cause health effects both in allergic and non-allergic people. The health effects consistently associated with indoor dampness and molds include:

  • Allergic rhinitis (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
  • Asthma attacks in those who already have asthma
  • Causation of new asthma
  • Respiratory infections such as acute bronchitis
  • Eye irritation (burning, watery, or reddened eyes)
  • Eczema, and skin rashes or irritation

Mold and Habitability

To our knowledge, "mold" has never been explicitly listed as a habitability issue for California rental property in code or regulation. Legislation in 2001 attempted to establish a "bright-line" for unacceptable levels of indoor mold and guidelines for assessment, clean-up, and disclosure. In fact, guidance on mold issues has evolved among experts in the field over the past decade.

2001 Toxic Mold Protection Act

The 2001 Toxic Mold Protection Act (SB 732, Ortiz) directed the California Department of Health Services (now Department of Public Health or CDPH) to establish various programs to develop guidelines for mold assessment, clean-up, and disclosure in residences. However, these components were dependent on the Department establishing health-based, permissible exposure limits (or PELs). In April 2005, CDPH released its "Report to the California Legislature on Implementation of the Toxic Mold Protection Act of 2001," of which one of the key findings was

"After considerable research into this question, [CDPH] staff has determined that sound, science-based PELs [health-based standards] for indoor molds cannot be established at this time."

It continues

".. [CDPH] 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 view was reaffirmed in the Department's July 2008 update. The 2005 report and 2008 update are available on-line:



It is worth noting that after passage of SB 732 in 2001, insurance providers began including notification to policy holders that damage caused by mold may be limited or excluded from their coverage.

2011 CDPH Statement

Last year, the Department released a "Statement on Building Dampness, Mold, and Health," which states

"CDPH has concluded that the presence of water damage, dampness, visible mold, or mold odor in schools, workplaces, residences, and other indoor environments is unhealthy. We recommend against measuring indoor microorganisms or using the presence of specific microorganisms to determine the level of health hazard or the need for urgent remediation. Rather, we strongly recommend addressing water damage, dampness, visible mold, and mold odor by (a) identification and correction of the source of water that may allow microbial growth or contribute to other problems, (b) the rapid drying or removal of damp materials, and (c) the cleaning or removal of mold and moldy materials, as rapidly and safely as possible, to protect the health and well-being of building occupants, especially children."

CDPH's position is consistent with the current consensus among scientists and medical experts (cited in the Statement) that

  • Visible water damage, damp materials, visible mold, and mold odor indicate an increased risk of respiratory disease
  • The traditional methods used to measure mold exposure do not reliably predict health risks
  • The differentiation of some molds (such as Stachybotrys species) as "toxic molds" that are especially hazardous to healthy individuals is not justified
  • The most important steps in dealing with indoor dampness or mold are to identify the source of moisture and to take the necessary steps to make repairs to stop them

Other Advice for Occupants of Water-Damaged or Moldy Buildings

The California Department of Consumer Affairs offers in its most recent guidance for tenants (California Tenants - A Guide to Residential Tenants' And Landlords' Rights And Responsibilities) that

"... the presence of mold conditions in the rental unit that affect the livability of the unit or the health and safety of tenants" may be a way in which the implied habitability of a unit is violated and that a tenant may be able to claim a breach of the implied warranty on the basis of documented contamination.

See page 39 http://www.dca.ca.gov/publications/landlordbook/catenant.pdf

The Code Enforcement Workgroup of the California Healthy Housing Coalition is discussing how to deal with dampness-related complaints in rental housing


Additional reliable resources on mold are available from

Last modified on: 5/15/2014 11:28 AM