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Molds are types of fungi found throughout the natural environment. Molds reproduce by generating tiny, microscopic spores, just like how plants reproduce by producing  seeds.

Mold spores can be found in both indoor and outdoor air, as well as settled on indoor and outdoor surfaces. In the outdoors, molds live in the soil, on plants, and on dead or decaying organic matter. They play an important and natural role in the breakdown of leaves, wood, and other plant debris.

However, when molds grow indoors, they can damage building materials, furnishings, clothes, and other organic materials. They can also cause respiratory and other health problems for building occupants. 

Image of mold

Molds can grow on virtually any substance, as long as moisture and oxygen are present. There are molds that can grow on wood, paper, carpet, foods, and insulation.

Molds need three things to grow:

  1. A wet or damp environment.

  2. A food source such as leaves, wood, paper products, wall board, insulation materials, ceiling tiles, and other organic based materials.

  3. A temperature range similar to the average residential household temperature.

10 Things to Remember about Mold:

  1. Potential health effects and symptoms associated with mold exposure include allergic reactions, asthma, and other respiratory complaints.

  2. There is no practical way to eliminate all mold and mold spores in the indoor environment; the way to control indoor mold growth is to control moisture.

  3. If mold is a problem in your home or school, you must clean up the mold and eliminate sources of moisture.

  4. Fix the source of the water problem or leak to prevent mold growth.

  5. Reduce indoor humidity (to 30-50%) to decrease mold growth by: venting bathrooms, dryers, and other moisture-generating sources to the outside; using air conditioners and de-humidifiers; increasing ventilation; and using exhaust fans whenever cooking, dishwashing, and cleaning.

  6. Clean and dry any damp or wet building materials and furnishings within 24-48 hours to prevent mold growth.

  7. Clean mold off hard surfaces with water and detergent, and dry completely. Absorbent materials such as ceiling tiles may need to be replaced.

  8. Prevent condensation and reduce the potential for condensation on cold surfaces (i.e., windows, piping, exterior walls, roof, or floors) by adding insulation.

  9. In areas where there is a perpetual moisture problem, do not install carpeting (i.e. by drinking fountains, by classroom sinks, or on concrete floors with leaks or frequent condensation).

  10. Molds can be found almost anywhere; they can grow on virtually any substance, providing moisture is present. There are molds that can grow on wood, paper, carpet, and foods.

                                                            Image of Common areas for Mold in Homes

Essential Readings and Useful Links on Mold:


Health Effects of Mold Exposure

Exposure to molds does not always cause health problems. However, some people are sensitive to molds and are at risk for potential negative health effects. Public safety is the most important reason to prevent mold growth and to address any existing indoor mold.

Health effects from exposure to mold vary greatly depending on the person and the amount of mold present.

Symptoms may include coughing, wheezing, and nasal and throat conditions. People with asthma or allergies who are sensitive to mold may notice their asthma or allergy symptoms worsen. Individuals with severely weakened immune systems who are exposed to mold are at risk of developing serious fungal respiratory infections.

Individuals that may be particularly sensitive to mold include:

  • Infants and children

  • Seniors

  • Individuals with respiratory conditions or sensitivities such as allergies or asthma.

  • Individuals with severely weakened immune systems (for example, people with HIV infection, chemotherapy patients, or organ transplant recipients)

It is important to consult a medical professional if you are concerned about the potential health effects of mold exposure.


Image of Mold under sink

Mold Toxins

Recent media reports have popularized the term "toxic mold." According to the Center for Disease Control and Prevention, the term "toxic mold" is not accurate. While certain molds are toxigenic, meaning they can produce toxins (specifically mycotoxins), the molds themselves are not toxic or poisonous.

There are very few reports that toxigenic molds found inside homes can cause unique or rare health conditions, and a causal link between the presence of the toxigenic mold and these conditions has not been proven. Hazards presented by molds that may produce mycotoxins should be considered the same as other common molds, and efforts should be made to prevent the growth of all types of molds.


Preventing Mold

Molds need both food and water to survive; since molds can digest most things, water is the factor that limits mold growth. Molds will often grow in damp or wet areas indoors.  

Moisture control is the key to mold control.

Common sites for indoor mold growth include areas where water and humidity may be present, including:

  • Bathrooms

  • Kitchens

  • Basement Walls

  • Around windows and doors (particularly glass doors)

  • Anywhere moisture condenses

Mold on Sliding Glass Door

Mold and Building Materials

Many building materials contain the nutrients necessary for mold growth. Wet cellulose (plant material) materials, including paper and paper products, cardboard, ceiling tiles, wood, and wood products, are particularly conducive for mold growth, as are drywall, carpet, fabric, and upholstery.

Common sources or causes of water or moisture problems include:

  • Roof leaks

  • Condensation associated with high humidity or cold spots in a building

  • Localized flooding due to plumbing failures or heavy precipitation or melting snow

  • Malfunctioning or poorly designed ventilation or humidification systems


Uncontrolled humidity can also be a source of moisture leading to mold growth, particularly in hot, humid climates. Recent changes to building codes have included increased emphasis on making sure buildings are tightly sealed to conserve energy. It is important that tightly sealed buildings also have adequate ventilation systems to ensure a sufficient quantity of fresh air is introduced into the occupied space, and that humidity levels are appropriately controlled.

Other than controlling obvious moisture problems, maintaining heating, air conditioning, and ventilation systems in proper working order is the best way to minimize the potential for mold growth indoors.


Eliminating Mold

The U.S. Environmental Protection Agency has several publications that provide excellent guidance on mold cleanup in homes, offices, and institutional facilities.

image of attempting to remove Mold
  • The publication "A Brief Guide to Mold, Moisture, and Your Home" provides information on a variety of things to consider when cleaning up mold, including when to consider utilizing a professional mold remediation contractor. 

  • If the services of a professional remediation contractor are required, the publication "Mold Remediation in Schools and Commercial Buildings" is a comprehensive guidance document for large scale cleanup efforts. Although this publication focuses on schools and commercial buildings, it is applicable to buildings of all types.

Finding a Licensed Mold Contractor

Information on finding a professional to perform mold cleanup can be found at Finding an Indoor Air Quality Professional

Image of Mold on Suitcase

The Maryland Mold Remediation Services Act

In 2008, the Maryland General Assembly passed the Maryland Mold Remediation Services Act. This law requires that any company or firm that provides mold remediation services on residential property in Maryland obtain a license to provide mold remediation services. In addition the law requires that each employee who provides mold remediation services be certified by an accreditation body as a microbial remediation technician or supervisor, whichever is applicable.

This license is to be issued by the Maryland Home Improvement Commission (MHIC), an agency within the Department of Labor, Licensing and Regulation (DLLR). The license to provide mold remediation services is different from the MHIC license for a contractor, subcontractor, or salesperson.

This law was scheduled to take effect on July 1, 2013. However, due to budget constraints, the DLLR has postponed the implementation of the law indefinitely. Therefore, until the Mold Remediation Services Act is implemented, a mold remediation contractor who only performs "cleaning" type services (such as cleaning ventilation systems or applying chemicals to kill mold), would not be required to hold a MHIC license.

Any mold remediation contractor who performs structural renovations to a house in the course of a mold remediation project (for example, tearing out and rebuilding walls, repairing drywall, replacing floors, etc.) is required to hold a MHIC contractor license.

Once the law is implemented, any contractor that currently holds a MHIC contractor or subcontractor license and who also provides mold remediation services on residential properties will be required to hold both the contractor and subcontractor license and the license to provide mold remediation services.


Mold Regulations

Currently, there are no federal, state, or county regulations for airborne mold contaminants, and standards for an acceptable or tolerable quantity of mold or mold spores have not been established.

As a result, organizations like the Centers for Disease Control and Prevention do not recommend routine sampling for molds.

Generally, it is not necessary to identify the species of mold growing in a building because this is not a reliable indicator of an individual’s health risk.  There is so much variability in the way people are affected by mold, as well as the types of mold, that it would be unnecessarily expensive and take a lot of time. If mold is seen or smelled, there is a potential health risk, and steps should be taken to remove the mold. Furthermore, reliable sampling for mold can be expensive.

Surface sampling may be useful to determine if an area has been adequately cleaned or remediated.  Sampling for mold should be conducted by professionals who have specific experience in designing mold sampling protocols, sampling methods, and interpreting results. 


Mold inside wall cavityCounty Building Standards – Mold in a Rental Property

Chapter 26 of the Montgomery County Code requires that property owners maintain a rental space free from water damage and mold. If you have concerns about mold in your rental property, contact your landlord for assistance.

If your landlord fails to address the problem, you may register a complaint with the Department of Housing and Community Affairs by contacting the County’s Customer Service Center at 240-777-0311 or by filing a complaint on-line at Enter the keywords “housing complaint” in the search box and click on the “Housing Complaints” link.