California Department of Public Health (CDPH) SOURCE
Indoor Air Quality (IAQ) Info Sheet 

Mold in My Home—What Do I Do?

Updated July 2012 

This info sheet provides basic information on water damage in the home. It describes molds, why they may grow indoors, 
health concerns related to mold exposure, the detection and prevention of indoor mold, and cleanup procedures for mold-
contaminated materials with reference to additional resources and documents. 


What are molds? 

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 recycle 
nutrients in the environment. 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. Sometimes, new molds even grow on old mold 
colonies. 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. 

How am I exposed to indoor molds? 

Molds release countless, tiny spores, which travel 
through the air. Everyone inhales some mold every day 
without apparent harm. It is common to find mold spores 
in the air inside homes. In fact, most of the airborne spores 
found indoors come from outdoor sources. Mold spores 
primarily cause health problems when they are present in 
large numbers and exposure is high. This may occur when 
there is active mold growth within a home, office, school, 
or other building in which people live or work for long 
periods. People also can be exposed to mold by touching 
contaminated materials and by eating contaminated foods. 

Can mold become a problem in my home? 

Yes. Molds will grow and multiply whenever 
conditions are right, that is, when sufficient moisture is 
available and organic matter is present. Be on the lookout 
for the following common sources of moisture inside and 
outside your home that may lead to mold problems: 

• Leaky roof 
• Sprinkler spray hitting the house 
• Plumbing leaks or overflow from sinks or sewers 
• Damp basement or crawl space 
• Humidifiers or steam from showers or cooking 
• Wet clothes hung indoors 
or a clothes dryer that 
exhausts indoors 
July 5, 2012 

Warped floors and stains on walls and ceilings can be 
indications of moisture problems. Condensation on 
windows or walls also is an important sign of excessive 
dampness and can be caused by some of the sources listed 
above. However, condensation also can be caused by an 
indoor combustion problem. Therefore, inspect fuel-
burning appliances annually, and contact your local utility 
or a professional heating contractor if you have questions. 
General information on gas appliance safety is available at: 


Should I be concerned about mold in my 

Yes, if indoor mold contamination is extensive, it can 
lead to very high and persistent exposures to airborne 
spores. Persons exposed to high spore levels can become 
sensitized and develop allergies to the mold or they may 
develop other health problems (see below). 

Mold growth also can damage your furnishings, such 
as carpets, chairs and sofas, and cabinets. Clothes and 
shoes in damp closets can become soiled and start to fall 

Unchecked, mold growth can seriously damage the 
structural elements in your home, for example, floors, 
walls, and ceilings. 


What symptoms can mold cause? 

Molds produce health effects through 
inflammation, allergy, or infection. Allergic reactions 
(often referred to as hay fever) are the most common 
responses following mold exposure. Known health 
risks from mold exposure include: the development of 
asthma, allergies, and res-piratory infections; the 
triggering of asthma attacks; and increased wheeze, 
cough, difficulty breathing, and other symptoms. In 
addition, evidence is accumulating, although not yet 
conclusive, that the more extensive, widespread, or 
severe the water damage, dampness, visible mold, or 
mold odor, the greater the health risks. 

CDPH has released a statement on building dampness, 

mold, and health that summarizes the evidence-based 

health risks from indoor dampness and mold. 


How much mold can make me sick? 

It depends. For some people, a relatively small number 
of mold spores can trigger an asthma attack or lead to other 
health problems. For other persons, symptoms may occur 
only when exposure levels are much higher. Nonetheless, 
indoor mold growth is unsanitary and 
undesirable. Basically, if you can see or smell mold, 
identify and eliminate excess moisture, and cleanup and 
remove the mold (see below). 

Anyone with a health problem they believe to be 
due to mold should consult a medical professional. 

Are some molds more hazardous than 

Perhaps. Allergic persons vary in their sensitivities to 
mold, both as to the amount and the types to which they 
react. In addition to their allergic properties, certain types 
of molds (such as Stachybotrys chartarum) may produce 
compounds with toxic properties known as mycotoxins. 

A mold may not always produce mycotoxins, 
depending on the material on which it is growing, the 
indoor temperature or humidity, the pH of the material, or 
other, as yet unknown, factors. When produced, mycotoxins 
may be present in both living and dead spores as 
well as materials that were contaminated with mold. 

A wet layer encloses S. chartarum spores while they 
are growing, preventing them from readily becoming airborne. 
However, when the mold dries up, air currents or 
physical handling can release spores into the air. 

At present there is no environmental test to determine 
whether S. chartarum found in buildings is producing 
toxins, nor can blood or urine tests establish that an individual 
has been exposed to S. chartarum spores or toxins. 

Additional fact sheets on mold and health effects, 
including specifically Stachybotrys, are available from the 
CDPH Environmental Health Investigations Branch web-

Health Effects of Toxin-producing Molds in California 
Fungi and Indoor Air Quality 
Stachybotrys chartarum (atra) — A mold that may be 
found in water-damaged homes 
Misinterpretation of Stachybotrys Serology 
The Centers for Disease Control and Prevention (CDC) 
also has information at 
(Facts about Stachybotrys chartarum and Other Molds). 

Are some persons at greater risk if exposed 
to mold? 

Exposure to building-related mold is not healthy for 
anyone. Therefore, it is best to identify and correct high 
moisture conditions quickly, before mold grows and health 
problems develop. 

Some persons may have more severe symptoms or 
become ill more readily than others: 

Individuals with existing respiratory conditions, such 
as allergies, chemical sensitivities, or asthma 
Persons with weakened immune systems (such as HIV 
infected persons, cancer chemotherapy patients, and so 
Infants, young children, and older persons 

How can I tell if I have mold in my house? 

You may suspect that you have mold if you see discolored 
patches or cottony or speckled growth on walls or furniture 
or if you smell an earthy or musty odor. You also may 
suspect mold contamination if mold-allergic individuals 
experience some of the symptoms listed above when in the 
house. Evidence of past or ongoing water damage also 
should trigger a more thorough inspection for damp 
conditions. You may find mold growth underneath water-
damaged surfaces (for example, wallpaper) or behind 
walls, floors, or ceilings. 

Should I test my home for mold? 

There is consensus among scientists and medical 
experts that the traditional methods used to identify 
increased mold exposure do not reliably predict increased 
health risks. Therefore, CDPH recommends against 
measuring indoor microorganisms or using the presence of 
specific microorganisms to determine the level of health 
hazard or the need for urgent remediation. 

Reliable air sampling for mold can be expensive and 
requires expertise and equipment that is not available to the 
general public. Private home and apartment owners 
generally will need to hire a contractor, because insurance 
companies and public agencies seldom provide this service. 
Mold inspection and cleanup usually is considered a 
housekeeping task that is the responsibility of a homeowner 
or landlord, as are roof and plumbing repairs, house 
cleaning, and yard maintenance. 

The simplest way to deal with a suspicion of mold 
contamination is: 

If you can see or smell mold, you likely have a 

problem and should take the steps outlined below to 

correct it. 

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The following information is intended as an overview 
for homeowners and apartment dwellers. For further 
details, consult the more thorough documents listed in the 

Judging how large a problem you have 

Small mold problems—total area less than 10 square 
feet can be handled by the homeowner or apartment 
maintenance personnel using personal protective equipment 
(see below). Large contamination problems—areas 
greater than 100 square feet may require an experienced, 
professional contractor. For in-between cases, the type of 
containment and personal protection will be a matter of 

What can I save? What should I toss? 

Discard items from which it will be difficult to remove 
mold completely. Solid materials generally can be kept 
after they are thoroughly cleaned. 

• First, fix the moisture problem and remove excess water. 
• A wet/dry vacuum cleaner may help remove water and 
clean the area. 
• Discard porous materials, for example, mold-damaged 
ceiling tiles, drywall or wallboard, carpeting, drapes, 
upholstered furniture, and wood products. Spores are 
more easily released when moldy materials dry out, 
therefore, remove moldy items as soon as possible. 
• Contain the area in which you work to reduce the spread 
of dust to other areas, for example, close the door or use 
plastic sheets to separate the room and run a suction fan 
that exhausts the air outdoors. 
• Remove drywall to a level above the high-water mark. 
Visually inspect the interior, and remove any mold-
contaminated material, such as insulation. 
• Carpet is often difficult to clean thoroughly, especially 
when the backing or padding is moldy, in which case it 
should be discarded. 
• If properly bagged or enclosed, mold-contaminated items 
can be discarded with household trash. 
• Clean nonporous materials, for example, glass, plastic, 
metal, and ceramic tiles 
• Wear gloves, an N-95 respirator, and eye protection. 
• Use a non-ammonia soap or detergent, or a commercial 
cleaner, in hot water, and scrub the entire mold-affected 
• Use a stiff brush or cleaning pad on cement-block walls 
and other uneven surfaces. 
• Rinse cleaned items with water and dry thoroughly. 
Disinfection of contaminated materials 

Disinfecting agents can be toxic for humans as well as 
molds; therefore, they should be used only when necessary 
and should be handled with caution. Disinfectants should 
be applied only to thoroughly cleaned materials to ensure 
that the mold has been killed. 

• Wear gloves and eye protection when using disinfectants 
and ventilate the area well. 
• A 10% solution of household bleach can be used as a 
disinfectant. Use 1½ cups of household bleach per gallon 
of water. 
• When disinfecting a large structure, make sure that the 
entire surface is wetted, for example, the floors, joists, 
and posts. 
• Keep the disinfectant on the treated 
material for the 
prescribed time before rinsing or drying – 10 minutes 
typically is recommended for a bleach solution. 
• Properly collect and dispose of extra disinfectant and 

Do not use disinfectants instead of, or before, 
cleaning nonporous materials with soap or detergent. 

Bleach straight from the bottle is actually LESS 
effective than diluted bleach. 

Never mix bleach with ammonia because this may 
produce toxic fumes. 

Bleach fumes can irritate the eyes, nose, and throat, 
and spilled bleach can irritate skin and damage 
clothing and shoes. 


Eye Contact: Hold eye open and rinse with water for 15– 
20 minutes. Remove contact lenses, after first 5 
minutes. Continue rinsing eye. Call a physician. 

Skin Contact: Wash skin with water for 15–20 minutes. If 
irritation develops, call a physician. 

Ingestion: Do not induce vomiting. Drink a glassful of 
water. If irritation develops, call a physician. Do not 
give anything by mouth to an unconscious person. 

Inhalation: Remove to fresh air. If breathing is affected, 
call a physician. 

Can cleaning up mold be hazardous to my 

Yes. During the cleaning process, you may be exposed 
to mold, strong detergents, and disinfectants. Spore counts 
may be 10 to 1000 times higher than background levels 
when mold-contaminated materials are disturbed. 

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Take steps to protect your and your family’s health during 

• Use a respirator when handling or cleaning moldy 
materials to protect yourself from inhaling airborne 
• You can purchase respirators from 
hardware stores. 
Select an N-95 respirator that is effective for particle 
(particulate) removal. 
• Wear protective clothing that is easily cleaned or discarded 
• Use rubber gloves. 
• Clean a test area first. 
Beware that respirators that remove particles will not 
protect you from fumes, such as from bleach. When 
using bleach or other disinfectants, minimize 
exposure by ventilating the area well. 

If cleaning a test area bothered you, consider hiring a 
licensed contractor or other experienced professional to 
carry out the work. The California Department of 
Consumer Affairs (CDCA) provides information on how to 
hire a contractor and describes the different classifications 
of licensed contractors: 

What Kind of Contractor Do You Need? 

Licensing Classifications. 

• Ask family members or bystanders to leave areas that are 
being cleaned. 
• Work for short time periods and rest where you 
breath fresh air. 
• Air out your home well during and after the work. 
Never use a gasoline engine indoors (e.g., a water 
pump, pressure washer, or generator) as you could 
expose yourself and your family to toxic carbon 

Can air ducts become contaminated with 

Yes. Duct systems may be constructed of bare sheet 
metal, sheet metal with fibrous glass insulation on the 
outside, sheet metal with fibrous glass on the inside, or 
entirely of fibrous glass. Bare sheet metal systems and 
sheet metal with exterior insulation can be cleaned and 

Water-damaged fibrous glass liner often will need to 
be removed and discarded, and ductwork in difficult-toreach 
locations may have to be abandoned. If you have 
questions, contact an air duct cleaning professional or 
licensed contractor. 

Can ozone air cleaners help remove indoor 
mold or reduce odors? 

No. Ozone is not effective in controlling indoor molds 
and other microbial contamination, even at concentrations 
far above levels safe for humans. Ozone is a strong oxidizing 
agent and a known lung irritant and may damage 
materials in the home, for example, rubber items may 
become brittle. 

For these reasons, CDPH strongly recommends that 

you NOT use an ozone air cleaner in any occupied 

space. Refer to the Air Resources Board, Hazardous 

Ozone-Generating "Air Purifiers" 

A particle removing air cleaner should only be used as 
a short-term means to reduce mold exposure. The underlying 
moisture problem must be identified, and moldy 
materials must be removed or cleaned. 

How can I prevent indoor mold problems in 
my home? 

Inspect your home regularly for the signs and sources 
of indoor moisture and mold listed on page one. Take steps 
to eliminate water sources as quickly as possible. Act immediately 
if a leak or flooding occurs. 

Stop the source of leak or flooding. 
Remove excess water with mops or wet vacuum. 
Move wet items to a dry, well-ventilated area or place 
them outdoors to speed drying. 
Move rugs and pull up wet carpet as soon as possible. 
Open closet and cabinet doors and move furniture 
away from walls to increase circulation. 
Open wall cavities, remove baseboards, or pry open 
wall paneling, if necessary, to allow the area to dry 
Run portable fans to increase air circulation. 
Run dehumidifiers to remove moisture from the air. 
Depending on the time of year, determine if a window 
air conditioner or portable heater would help dry the 
Do NOT use the home’s central blower if it or any of 

the ducts were flooded because this could spread mold 

throughout the home. 

Do NOT use fans if mold has already started to grow 
as this also could spread mold. 

July 5, 2012 


Your city or county health department may be able to 

answer questions or provide assistance on handling mold 

problems. For links to local California health departments: 


Other information on local government programs is 
available at 


General Information 

U.S. Environmental Protection Agency. The Key to 
Mold Control is Moisture Control. 

U.S. Centers for Disease Control and Prevention. 
Mold Information. Information on mold and health; an 
inventory of state indoor air quality programs; advice 
on assessment, cleanup efforts, and prevention of mold 
growth; and links to resources. 

CDPH Occupational Health Branch. Mold in Indoor 
Workplaces. An overview with specific resources for 

California Research Bureau. Indoor Mold: A General 
Guide to Health Effects, Prevention, and 
Remediation. A report to the California legislature. 

New York City Department of Health. An overview and 
info sheets on Facts About Mold, Flood Fact Sheet, 
Healthy Homes: Facts About Mold, Healthy Homes: 
Mold Tear-Off, and Mold Guidelines. 

Health Canada. Fungal Contamination in Public 
Buildings: Health Effects and Investigation Methods 

Health Canada. Residential Indoor Air Quality 
Guidelines: Moulds (2007). Information on the 
Physical and Chemical Properties, Causes of Mold 
Growth, Health Effects, and the Canadian Guideline.

Mould, Dampness, and Humidity. Information on the 
Effects of Mould on Health, Mould: Get Rid of It, and 
Mould in Indoor Air.

Clean-up Guidance 

U.S. Environmental Protection Agency. Mold 
Remediation in Schools and Commercial Buildings. 
Also applicable to residences. 

U.S. Centers for Disease Control and Prevention. 
Prevention and Remediation Strategies for the 

Control and Removal of Fungal Growth. 

American Red Cross/Federal Emergency Management 
Agency. Repairing Your Flooded Home. Guidance for 
recovery after flooding disasters addressing technical 
and logistical issues 

New York City Department of Health. Guidelines on 
Assessment and Remediation of Fungi in Indoor 

Consultants, Laboratories, and Clinics 

CDPH Listing of Consultants Offering IAQ Services in 
California. Self-reported database of contractors and 
advice on using the list.
find-a-contractor and http://www.caliaq.

American Industrial Hygiene Association. Listing of 
laboratories accredited in environmental microbiology. 

Association of Occupational and Environmental Clinics. 

Directory of clinics in California and other states. 


CDPH Indoor Air Quality Section 
Chief: Dr. Kazukiyo Kumagai 
850 Marina Bay Parkway (EHLB) 
Richmond, CA 94804-6403. 


Edmund G. (Jerry) Brown, Governor 
State of California 
Diana S. Dooley, Secretary 
Health and Human Services Agency 
Ron Chapman, M.D., M.P.H., Director 
Department of Public Health 

© California Department of Public Health, 2012 

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