Mold refers to a large diverse group of fungal organisms that grow in filaments, resulting in a cottony, fuzzy appearance, and reproduce by forming spores. They grow on organic substances and other surfaces where moisture is present. They especially thrive in damp, warm environments. Molds that grow in shower stalls and bathrooms and that are white or gray in color are sometimes referred to as mildew.

Tiny mold spores are not visible to the naked eye. They are persistent, can be transported through the air, and can survive in conditions that molds cannot grow, such as dry environments. When mold spores land on a surface where moisture is present, the mold then starts to grow.

Molds are found both outdoors and indoors. Outdoors molds aid in the decomposition of organic matter such as dead trees, compost, and leaves. The most common types of indoor household mold include Cladosporium, Penicillium, Stachybotrys, Alternaria, and Aspergillus.

A specialist in combating mold in an apartment.

A specialist in combating mold in an apartment.

Indoor molds can also destroy surfaces and objects on which they grow.


Molds (fungi) are present almost everywhere. Molds can be many different colors and produce a musty odor. In an indoor environment hundreds of different kinds of mold are able to grow wherever there is moisture and an organic substrate, which serves as a food source. They can grow on building and other materials, including: the paper on gypsum wallboard (drywall), ceiling tiles, wood products, paint, wallpaper, carpeting, some furnishings, books/papers, clothes, and other fabrics. Mold can also grow on moist, dirty surfaces such as concrete, fiberglass insulation, heating and air conditioning ducts, and ceramic tiles. It is not possible to eliminate the presence of all indoor fungal spores and fragments; however, mold growth indoors can and should be prevented and removed as much as possible, for molds have been associated with human health effects in persons allergic to molds. Molds produce irritating substances that may act as allergens, and some molds produce toxic substances called mycotoxins.

Moisture in a building may come from a variety of sources, such as leakage or seepage through basement floors, showering, and cooking. The amount of moisture that air can hold is dependent on the temperature of the air, with colder air being able to hold less moisture than warmer air. This moisture can cause mold to grow. Mold can especially be troublesome after a building has been exposed to flooding.


The prevalence of indoor dampness varies widely within and among countries, continents and climate zones. It is estimated to affect 10–50% of indoor environments in Europe, North America, Australia, India and Japan. In some areas, such as river valleys and coastal areas, the conditions of dampness can be substantially more severe.

Except in buildings with extensive mold growth, the amount of mold found in indoor air is usually much less than what is found outdoors. For people with allergies to mold, however, there may be no practical level of exposure, either indoors or outdoors, that would not create discomfort or harm. It is therefore wise to remove and prevent indoor mold growth.

Causes and symptoms

For persons who are sensitive to molds, exposure may result in nasal stuffiness and sneezing, eye irritation, wheezing, coughing, sinus problems, fatigue, skin irritation, and headaches or migraines. Exposure to molds can trigger asthma episodes in persons with asthma. Allergic individuals vary in their degree of susceptibility to mold, with the severity of an allergic response depending on the extent and type of mold that is present.

Persons with chronic lung illnesses, such as obstructive lung disease or persons with severely weakened immune systems, including those with transplants, chemotherapy, AIDS, and newborn infants, may develop other diseases such as allergic bronchopulmonary aspergillosis, an allergic lung reaction to a type of fungus (most commonly Aspergillus fumigatus) that occurs in some people with asthma or cystic fibrosis, and hypersensitivity pneumonitis, an inflammation of the lung (usually of the very small airways) caused by the body's immune reaction to small air-borne particles, including molds, and resulting in fever, chills, coughing, shortness of breath, and body aches.

There is no consensus on how significant a threat that inhalation of molds in residential, school, or office settings are to human health, except to persons who are allergic to mold. Building-related illnesses are often difficult to diagnose and interpret, for symptoms are nonspecific and often allergy-related, and it is difficult to make conclusive links to environmental factors.


Diagnosis of mold infestations

The U.S. Environmental Protection Association (EPA) has stated that if visible mold is present, testing is usually unnecessary. No standards have been established for mold or mold spore levels, since tolerable or acceptable limits of mold exposure for humans have not been defined. Individuals vary in their susceptibility to mold, so testing and measurement of mold presence is not effective in predicting the degree of health risks from an occurrence of mold.

Therefore, a mold infestation is determined primarily on visual assessment, knowledge of the building structure, and the history of water damage in the building.

Diagnosis of diseases associated with mold infestations

To diagnose an allergy to mold or fungi, the medical practitioner must take a complete medical history. If mold allergy is suspected, the doctor may do skin tests, where extracts of different types of fungi will be used to scratch or prick the skin. If there is no reaction, allergy is not likely. In some people with allergy, irritation alone can cause a reaction, so it may not actually be an allergic reaction. Therefore the medical practitioner combines the patient's medical history, the skin testing results, and a physical examination to diagnose a mold allergy.


Treatment of a mold infestation

Visible fungal growth represents unnecessary exposure and should not be present in indoor spaces. Visible fungus indicates improper moisture management in the building.

The first step in treatment of mold is to identify and repair the moisture problem. Mold will not grow unless sufficient moisture is present. Small amounts of mold growing on visible surfaces can usually be easily cleaned without professional assistance. Larger amounts of mold may require more extensive evaluation, repair or replacement, and dust control by professionals.

There are several methods available to clean up mold, depending on the size and type of surfaces affected. The work area can be cleaned using wet methods such as wet wiping with a detergent solution. In some cases, a dilute solution of chlorine bleach (no stronger than 1 cup of bleach in 1 gallon of water) or stronger commercial cleaners may be needed to kill the mold, for moldy surfaces should not be touched with bare hands. When washing with detergent and water, the use of rubber gloves is recommended. For bleach or harsher cleaning agents, nonporous gloves such as neoprene, nitrile, polyurethane, or PVC, should be worn along with protective eyewear. An N-95 respirator is recommended to limit exposure to airborne mold or spores during the cleaning process.

How to get rid of mold

How to get rid of mold

It is important to control dust associated with the clean-up activity. Dust should be controlled using damp cleaning methods and by using HEPA vacuuming. HEPA (High Efficiency Particulate Air) means that the vacuum filter is capable of removing particles that are 0.3 microns (one millionth of a meter) in diameter at 99.97% efficiency. Typical vacuum filters will not capture spores as efficiently and may disperse them in air. When the size of the area with visible mold growth is large or when sensitive people are present, the work area should be enclosed in plastic. The air inside the enclosure should be actively exhausted to the outdoors by placing the enclosed environment under negative pressure with respect to the rest of the room or building. If there are any leaks in the enclosure, that air will move from the cleaner areas outside the enclosure into the enclosure, and minimize air movement in the opposite direction.

When porous, cellulose-containing items such as drywall, clothing, carpets and carpet pads, textiles, upholstered furniture, leather, paper goods, and many types of artwork or decorative items get wet, they should be dried and disinfected within 48 hours or discarded. If sewage or gray water is involved, the materials should be discarded. These types of damp materials are usually the determining factor, rather than indoor humidity, are usually the primary determining factor whether mold growth will be excessive. Care should be taken to avoid that items not discarded become sources of re-infestation.

Treatment of diseases associated with mold

Since molds are common and it is difficult to avoid exposure, there are medications that may be used to alleviate allergic symptoms. These include:

Other treatments for mold allergy include:

A doctor may recommend additional treatments if affected individuals have mold-induced allergic bronchopulmonary aspergillosis and hypersensitivity pneumonitis.

Public health role and response

The public health community in most cases does not recommend evacuation in response to a mold infestation. There is no established level of airborne mold that is accepted as unsafe for the general population. However evacuation may be warranted for sensitive populations, such as infants, elderly, the immune-suppressed, and those with medically confirmed symptoms related to mold exposure.

A substance, such as mold, that causes an allergy.
Extra sensitivity of the body to certain substances, such as pollens, foods, molds, or microorganisms, that produces an immune responses and that results in symptoms such as sneezing, itching, and skin rashes.
A group of fungi known as major plant pathogens and as common allergens in humans. They grow indoors and can cause hay fever or extra sensitive reactions that can lead to asthma. They can also cause infections in persons who are immunocompromised.
Agroup of several hundred mold species found in various climates worldwide, some of which are important medically and commercially while others cause infection in humans and other animals.
A chronic long-lasting inflammatory disease of the lung airways, where the inflammation causes the airways to spasm and swell periodically so that the airways narrow. The individual wheezes or gasp for airs until the obstruction to air flow either resolves spontaneously or responds to a wide range of treatments. Continuing inflammation makes the airways extra sensitive to stimuli such as cold air, exercise, dust mites, molds, pollutants in the air, and even stress and anxiety.
A group of fungi that includes some of the most common indoor and outdoor molds. Their spores are wind-dispersed and are often extremely abundant in outdoor airs. They can grow on surfaces when moisture is present. The airborne spores are significant allergens and in large amounts they can severely affect asthmatics and people with respiratory diseases. Prolonged exposure may weaken the immune system.
A group of organisms with a membranebound nucleus that derive their nourishment from dead or decaying organic matter. The group includes mushrooms, yeasts, mildew, and molds. They have rigid cell walls but lack chlorophyll.
Incapable of developing a normal immune response, usually as a result of disease, malnutrition, or immunosuppressive therapy.
Immunoglobulin E—
A class of antibodies produced in the lungs, skin, and mucous membranes that are responsible for allergic reactions.
N-95 respirator—
Most common of the types of particulate filtering face piece respirators. It filters at least 95 percent of airborne particles but is not resistant to oil.
A group of fungi of major importance in the natural environment as well as in food and drug production. Members of the genus produce penicillin, which is used as an antibiotic to kill or stop the growth of certain kinds of bacteria in the body. Penicillium is a common indoor mold, and its spores can cause mold allergy.
A group of molds with widespread distribution that inhabit materials high in cellulose. Certain species are known as “black mold” or “toxic black mold” in the U.S. and are frequently associated with poor indoor air quality arising from fungal growth on water-damaged building materials. Some species produce mycotoxins that are known to produce health symptoms, but it is not scientifically clear whether these mycotoxins affect human health during a mold infestation in a building.

It is important that public health officials effectively communicate the effects of indoor mold exposure to the public. The key messages that should be conveyed are: the ubiquitous nature of fungi in the environment, the relative community of fungi found indoors compared to outdoors, the relative risk posed by the molds detected, and the range of options available to confront the problem.

Recent years have seen increased attention placed on mold-infested schools. Mold infestation in schools presents a special case in risk management and a challenge for public health officials, for parents usually have a low tolerance for either actual or perceived risk and are often organized and active in school issues.


Because people vary greatly in their immune response to environmental allergens, and because fungi are always present in the environment, it may not be possible to manage airborne fungal particles at a level protective of those individuals most sensitive to their allergenic effects. Therefore, molds are categorized with pollen, dander, and mite excrement as allergens to be managed but cannot be eliminated. When people present with allergic hypersensitivity, health effects due to mold are due more to individual sensitivity than to the presence or absence of exposure. However, to reduce exposure, mold infestations should be treated.


There is no practical way to eliminate mold and mold spores from an indoor environment. Therefore, to control or prevent the growth of mold, moisture levels within the building must be controlled. Methods of control include:


After moisture control has been completed, it may be necessary to remove and discard the materials that were affected by the mold.

See also Aspergillosis ; Asthma ; Fibrosis .



Billings, Kurt, and Lee Ann Billings. Mold: The War Within. Knoxville, TN: Partners Publishing LLC, 2010.

May, Jeffrey C., and Connie L. May. The Mold Survival Guide: For Your Home and for Your Health. Baltimore, MD: Johns Hopkins University Press, 2004.

Rosen, Gary. Environmentally Friendly Mold Remediation Techniques that Significantly Reduce Childhood Asthma. Naples, FL: Hope Academic Press, 2007.

Schaller, James, and Gary Rosen. Mold Illness and Mold Remediation Made Simple. Naples, FL: Hope Academic Press, 2006.


“Dampness and Mould” World Health Organization. .


Allergy and Asthma Foundation of America, 8201 Corporate Drive, Suite 1000, Landover, Maryland, USA, 20785, (800) 727-8462,,

Judith L. Sims

  This information is not a tool for self-diagnosis or a substitute for professional care.