Mold in Your Home

Mold is Common. Moisture is the Real Problem.

Mold is a type of fungus that grows wherever moisture is present. Tiny mold spores are naturally found both indoors and outdoors. When these spores land on damp surfaces, they can begin to grow.

Finding mold in your home does not automatically mean there is a serious health hazard, but it usually indicates a moisture problem that should be corrected. The best way to prevent mold is to control moisture and address water problems promptly.

Because mold is a natural part of the environment, it is impossible to eliminate mold spores completely. The goal is not to create a mold-free home, but to prevent the damp conditions that allow mold to grow indoors.

On This Page

• What is mold?

• Is mold dangerous?

• Health effects of mold

• What about “black mold”?

• Should I have my home tested?

• Preventing mold

• Cleaning mold

• Mold after flooding or major water damage

• When should I hire a professional?

• Mold and renters

• Frequently asked questions

• Understanding mold: A closer look

What Is Mold?

Mold is a general term used to describe many different types of fungi that grow in fuzzy, dusty, or discolored patches. Unlike familiar mushrooms, molds generally do not produce large, easily visible fruiting bodies.

Mold thrives in damp environments and can grow on many materials commonly found in homes, including:

• Wood

• Drywall

• Carpet

• Insulation

• Ceiling tiles

• Upholstered furniture

• Dust and organic debris

Mold reproduces by releasing microscopic spores into the air. These spores are naturally present throughout the environment and routinely enter homes through open doors and windows, ventilation systems, and on clothing, shoes, and pets.

When mold spores land on a surface with enough moisture, they can begin to grow.

Common sources of excess indoor moisture include:

• Plumbing leaks

• Roof leaks

• Flooding

• Condensation on windows or cold surfaces

• Poor ventilation

• High indoor humidity

• Water intrusion through walls or foundations

Addressing the source of moisture is the most important step in preventing mold from returning.

Is Mold Dangerous?

Not necessarily.

Most molds do not pose significant health hazards for healthy individuals. However, prolonged exposure to elevated mold levels may affect some people’s health or quality of life.

The effects of mold exposure vary considerably depending on factors such as:

• The type of mold present

• The amount of mold present

• How long a person is exposed

• An individual’s overall health and sensitivity

Some people may experience symptoms after relatively limited exposure, while others may experience no symptoms at all. Because people respond differently, there is no single level of mold exposure that can be considered harmful for everyone.

Rather than focusing on identifying the exact species, Kitsap Public Health District recommends addressing indoor mold by correcting the moisture problem and cleaning or removing the affected material.

Health Effects of Mold

Most people exposed to indoor mold experience either no symptoms or only mild irritation. When symptoms occur, they are often similar to seasonal allergies or irritation caused by dust.

Possible symptoms include:

• Sneezing

• Runny or stuffy nose

• Coughing

• Sore throat

• Sinus irritation

• Eye irritation

• Skin irritation

Exposure to elevated mold levels may trigger asthma symptoms or worsen existing asthma.

People with allergies, asthma, chronic lung disease, or weakened immune systems may be more likely to experience health effects.

It is important to remember that not everyone reacts to mold in the same way. A mold that causes symptoms in one person may have little or no effect on another.

People With Weakened Immune Systems

A small number of mold species can cause infections in people whose immune systems are severely compromised. This may include people receiving chemotherapy, organ transplant recipients taking immunosuppressive medication, or people with certain advanced immune disorders.

These infections are uncommon and are generally not a concern for healthy individuals. However, people with significantly weakened immune systems should use additional caution around mold and consult a healthcare provider if they have concerns.

Small Amounts of Mold

Small amounts of mold commonly found around windows, showers, bathrooms, plumbing fixtures, or other areas where condensation routinely occurs are generally unlikely to cause significant health problems when they are cleaned regularly and the area is kept as dry as practical.

What About “Black Mold”?

Many people have heard of “black mold,” but the term is often misunderstood.

Several different mold species can appear black. Some have been associated with greater health concerns than others, but mold cannot be identified by color or appearance alone.

Many common molds may appear black, dark green, gray, or brown. Some relatively low-risk molds can look nearly identical to species that have received greater public attention.

Because visual appearance is not a reliable way to identify mold, KPHD recommends treating all indoor mold in the same general manner:

• Correct the moisture problem.

• Clean or remove mold-contaminated material.

• Dry the area thoroughly.

• Take steps to prevent the mold from returning.

Whether mold appears black, green, white, gray, or another color does not change these basic recommendations.

Should I Have My Home Tested for Mold?

In most situations, mold testing is not necessary.

If visible mold is present, testing usually does not change what needs to be done. The priority should be to:

1. Find and correct the source of moisture.

2. Clean or remove the mold.

3. Dry the affected area.

4. Prevent the problem from returning.

Because mold spores naturally occur in both indoor and outdoor air, testing results can be difficult to interpret. The presence of spores does not necessarily indicate that a building has a serious mold problem or that mold is causing a person’s symptoms.

Testing may be appropriate in limited situations, including:

• Mold is suspected behind walls or above ceilings.

• A building has experienced extensive water damage.

• There are legal or insurance concerns.

• A qualified professional recommends testing as part of an investigation.

• A healthcare provider recommends environmental assessment.

  
  

For most homeowners and renters, correcting the moisture problem is more important than identifying the exact species of mold.

Preventing Mold

Because mold requires moisture to grow, mold problems are almost always moisture problems.

Preventing mold means identifying and controlling sources of excess moisture before mold has an opportunity to grow.

Common sources of moisture include:

• Plumbing leaks

• Roof leaks

• Flooding

• Condensation on windows and cold surfaces

• Poor ventilation

• High indoor humidity

• Water intrusion through walls or foundations

Tips for Preventing Mold

You can reduce the likelihood of mold growth by:

• Repairing plumbing, roof, and foundation leaks promptly.

• Using bathroom and kitchen exhaust fans while cooking or showering.

• Venting clothes dryers outdoors.

• Keeping indoor humidity as low as practical, generally below 50%.

• Using a dehumidifier in damp areas when needed.

• Wiping up condensation from windows and other cold surfaces.

• Allowing air to circulate throughout the home.

• Keeping furniture a few inches away from cold exterior walls when possible.

• Avoiding overcrowded storage in damp or poorly ventilated spaces.

• Drying wet materials as quickly as possible after spills or water damage.

Some condensation-related mold growth may be difficult to prevent completely, particularly during colder weather when warm indoor air contacts cold windows, walls, or ceilings.

Small amounts of recurring mold in bathrooms, around windows, or near plumbing fixtures can usually be managed through regular cleaning, improved ventilation, and moisture control.

Cleaning Mold

Small areas of mold can often be cleaned safely by homeowners.

Before cleaning mold, identify and correct the source of moisture. Cleaning mold without fixing the underlying water problem will usually result in the mold returning.

Cleaning Hard Surfaces

For mold growing on hard, nonporous surfaces:

1. Wear gloves and eye protection.

2. Clean the affected area using detergent and water or an appropriate household cleaner.

3. Follow the product manufacturer’s directions.

4. Dry the surface completely.

5. Continue monitoring the area to make sure the mold does not return.

In many situations, physically removing the mold is more important than the specific product used.

Porous Materials

Some porous materials cannot be effectively cleaned once mold has become established.

Materials that may need to be removed and replaced include:

• Drywall

• Ceiling tiles

• Carpet and carpet padding

• Insulation

• Upholstered furniture

• Other porous materials that remain damp or have extensive mold growth

Clothing, towels, and bedding can often be laundered if they have not been permanently damaged.

Painting or sealing over mold without first cleaning or removing the affected material and correcting the moisture problem is not recommended.

Mold After Flooding or Major Water Damage

Flooding, significant plumbing failures, and roof leaks can create conditions that allow mold to develop quickly.

The most important steps after water damage are to stop the source of the water and dry the affected area as soon as possible.

If your home has experienced flooding or significant water damage:

1. Stop the source of the water, if possible.

2. Remove standing water.

3. Dry affected materials using fans, dehumidifiers, and ventilation when conditions allow.

4. Remove and discard materials that cannot be completely dried.

5. Clean remaining surfaces before rebuilding or making repairs.

The longer building materials remain wet, the more likely mold growth becomes.

In severe cases, saturated drywall, insulation, carpeting, and upholstered furniture may need to be removed and discarded.

Water contaminated with sewage or other hazardous material requires additional precautions and may require professional cleanup.

When Should I Hire a Professional?

Many small mold problems can be safely managed by homeowners. Professional assistance may be appropriate when:

• Mold covers a large area.

• Mold returns repeatedly despite cleaning.

• The source of moisture cannot be identified or corrected.

• Heating, ventilation, or air-conditioning systems are affected.

• Sewage contamination is involved.

• Extensive flooding or water damage has occurred.

• Building materials are heavily saturated.

• Occupants have medical conditions that increase their risk from mold exposure.

• Mold may be hidden inside walls, ceilings, or other inaccessible areas.

A qualified mold remediation contractor can help identify moisture sources, recommend appropriate repairs, and safely remove extensive contamination.

KPHD does not license or certify mold contractors. Property owners should review qualifications, experience, references, and insurance before hiring a contractor.

Mold and Renters

Washington law requires landlords to provide tenants with information about controlling indoor mold growth and minimizing potential health risks.

Landlords are generally responsible for repairing building problems that allow water to enter a rental unit, including plumbing leaks, roof leaks, and structural problems that contribute to excess moisture.

Tenants should:

• Report leaks, flooding, or water damage promptly.

• Notify the landlord in writing when possible.

• Keep copies of maintenance requests and other communications.

• Use bathroom and kitchen exhaust fans when available.

• Maintain reasonable ventilation in the dwelling.

• Wipe up condensation when it occurs.

• Clean small amounts of condensation-related mold during normal housekeeping.

Washington’s Residential Landlord-Tenant Act, RCW 59.18, does not specifically require landlords to perform mold remediation in every circumstance. Responsibility often depends on the underlying cause of the moisture problem.

If mold results from a plumbing leak, roof leak, flooding, or another building maintenance issue, tenants should promptly notify the landlord so the underlying problem can be investigated and corrected.

KPHD does not enforce landlord-tenant law or resolve disputes between landlords and tenants. The Washington State Office of the Attourny General has resources available.

Frequently Asked Questions

Understanding Mold: A Closer Look

The information above answers the questions most homeowners and renters have about indoor mold.

The following sections provide more detailed information about mold biology, health effects, mycotoxins, and why mold species can be difficult to identify.

What Does “Mold” Mean Scientifically?

Mold is a general term for fungi that grow in dusty- or fuzzy-looking layers and that do not usually form familiar mushrooms or other large reproductive structures.

Like the word “shrub,” the word “mold” describes a growth pattern rather than a taxonomic relationship. Molds are not one closely related group of organisms. Instead, fungi from several different branches of the fungal family tree can grow in forms that people recognize as mold.

As a result, molds can vary widely in their lifecycles, chemistry, environmental roles, and relationships with humans.

For example, koji mold, Aspergillus oryzae, is used to make soy sauce and other fermented foods. It is more closely related to some mushroom-forming fungi than it is to black bread mold, Rhizopus stolonifer, which belongs to a different major group of fungi.

Molds can also be difficult to distinguish from other fungi, including rusts, smuts, and some yeasts.

The term “mold” therefore tells us relatively little about an individual species beyond its general appearance and preference for damp conditions.

Why Are Molds So Diverse?

Molds are found almost everywhere in nature. They play an important role in breaking down dead plants, wood, leaves, food, and other organic material.

Their spores can drift through the air or be carried indoors on clothing, shoes, pets, and objects. Once indoors, the spores may remain dormant unless they encounter enough moisture to germinate and grow.

Different mold species prefer different combinations of:

• Moisture

• Temperature

• Nutrients

• Light

• Air movement

• Surface material

Some molds grow readily on food. Others are more likely to grow on wood, drywall, insulation, fabric, or dust.

Because molds vary so widely, identifying a mold species does not automatically tell us whether it poses a health risk. The amount of exposure and the sensitivity of the exposed person are also important.

Why Mold Affects People Differently

Just as mushrooms range from edible to poisonous, molds vary significantly in their relationships with people.

Most molds do not cause serious illness in healthy individuals. However, exposure to prolonged or elevated mold levels may contribute to irritation, allergic symptoms, asthma symptoms, or reduced quality of life in some people.

People may react differently because of variations in:

• Allergy sensitivity

• Asthma

• Existing lung disease

• Immune system function

• The amount and duration of exposure

• The particular mold species present

A person who reacts strongly to one species may react only mildly, or not at all, to another.

It is also difficult to determine the exact level at which mold exposure becomes a health concern. Unlike some chemical contaminants, there is no single indoor mold level that clearly separates safe from unsafe conditions for every person.

This is one reason public health recommendations focus on preventing visible indoor mold growth rather than attempting to establish a universal exposure limit.

Opportunistic Mold Infections

A small number of molds can act as opportunistic pathogens.

An opportunistic pathogen usually causes disease only when a person’s immune defenses are significantly weakened. People who may be at increased risk include:

• Organ transplant recipients

• People receiving chemotherapy

• People taking strong immunosuppressive medication

• People with certain advanced immune disorders

• Some individuals with serious chronic lung disease

Although uncommon, opportunistic fungal infections can be serious or life-threatening.

These infections are generally not a concern for people with normally functioning immune systems.

People with significantly weakened immune systems should avoid disturbing extensive mold growth and should consult their healthcare provider for individualized guidance.

Mycotoxins

Molds produce many different chemical compounds as part of their growth and metabolism. Some of these compounds can be harmful to humans or animals and are collectively known as mycotoxins.

The health effects of certain mycotoxins are well established when contaminated food is eaten. Mycotoxin contamination of grains, nuts, and other foods is an important food-safety concern in many parts of the world.

The health effects of airborne exposure are less clear.

Research on exposure to spores or particles from mycotoxin-producing molds is more limited, and significant uncertainty remains about the risk posed by typical indoor airborne exposure.

The ability of a mold species to produce a mycotoxin also does not mean that it is producing the toxin in every environment. Toxin production may depend on temperature, moisture, nutrients, growth stage, and other environmental conditions.

Because these variables are difficult to evaluate in a home, practical recommendations remain the same: correct the moisture source and remove indoor mold growth.

The Science Behind “Black Mold”

“Black mold” is not a precise scientific term.

The phrase is often used to refer to Stachybotrys chartarum, and sometimes to other dark-colored molds such as Aspergillus niger. However, many unrelated mold species may appear black or very dark when viewed with the naked eye.

Stachybotrys chartarum can produce mycotoxins under certain growing conditions and has been associated with concerns about damp buildings and indoor air quality. However, there is ongoing scientific debate about the specific health effects caused by typical indoor airborne exposure.

Aspergillus niger is common in the environment and can grow on food and building materials. It can produce compounds that are harmful if consumed and may act as an opportunistic pathogen in susceptible individuals.

Other common molds, including species within the genus Cladosporium, can also appear black or dark and may be visually indistinguishable from molds that have received greater public attention.

For this reason, the color black does not establish that a mold is unusually hazardous.

Why Mold Cannot Be Identified by Appearance Alone

Color, texture, and growth pattern can provide clues, but they are not enough to reliably identify a mold species.

The same species may appear different depending on:

• The surface on which it is growing

• Moisture levels

• Temperature

• The age of the colony

• Lighting conditions

• The presence of other microorganisms

Different species may also look nearly identical.

Reliable identification may require microscopic examination, laboratory culture, or molecular methods such as DNA analysis.

Even when a species is identified, the result may not answer the most important practical questions:

• How much mold is present?

• How long have people been exposed?

• Is the mold actively growing?

• Is it producing harmful compounds?

• Is it causing anyone’s symptoms?

Because of these limitations, species identification is usually less important than finding and correcting the source of moisture.

KPHD’s Recommended Approach

Due to the wide variation among mold species, differences in individual sensitivity, and the difficulty of interpreting mold test results, KPHD recommends a precautionary and practical approach to indoor mold:

• Keep indoor mold growth to a minimum.

• Fix leaks and other moisture problems promptly.

• Clean small areas of mold when they appear.

• Remove materials that cannot be effectively cleaned or dried.

• Seek professional assistance for extensive or complicated mold problems.

• Consult a healthcare provider when health concerns are present.

The presence of mold does not automatically mean a building is dangerous. However, visible mold is evidence of excess moisture and should not be ignored.

Additional Resources

• Washington State Department of Health mold guidance

• U.S. Environmental Protection Agency mold and moisture resources

• Centers for Disease Control and Prevention mold information

• Washington Residential Landlord-Tenant Act

• Washington landlord mold information requirements