Inhalation exposure to mold indoors can cause negative health effects in some people. Molds produce allergens (substances that can cause allergic reactions), irritants and, in some cases, potentially toxic substances (mycotoxins). Inhaling or touching mold or mold spores may cause allergic reactions in sensitive individuals. Mold does not have to be alive to cause an allergic reaction in some people.

There are some specific groups of people who are potentially more easily or severely affected by mold than the average individual with no sensitivities to mold. They include infants, children, elderly people, individuals with respiratory conditions (such as allergies and asthma), and people with weakened immune systems (people with HIV/AIDS, chemotherapy patients, and organ transplant recipients).

Sensitive people should avoid areas that are likely to have mold, such as compost piles, cut grass and wooded areas.

Allergic reactions to mold in buildings do occur for many sensitive people. However, there is no conclusive evidence that proves that mold in a building directly causes illnesses in humans. More research is needed, and mold research has been continuous. Mold exposure as it relates to effects on human health is a complex and emerging science.

Symptoms of Mold Exposure

There are many symptoms of mold exposure. Current evidence indicates that allergies are the type of diseases most often associated with molds. An allergic reaction is the most common symptom, which could include wheezing and difficulty breathing.

According to the Centers for Disease Control, inhalation of fungal spores, fragments (parts), or metabolites (mycotoxins and volatile organic compounds) from a wide variety of fungi may lead to or exacerbate immunologic (allergic) reactions, cause toxic effects, or cause infections.

A single or repeated exposure to mold, mold spores, or mold fragments may cause non-sensitive individuals to become sensitive to mold, and repeated exposure has the potential to increase sensitivity. Allergic responses include “hay fever”-like symptoms, such as headache, sneezing, runny nose, irritated eyes, and skin rash (dermatitis). Molds can cause asthma attacks in people with asthma who are allergic to mold. Fungi in buildings may cause or exacerbate symptoms of allergies, especially in persons who have a history of allergic diseases (such as asthma and rhinitis). In addition, molds can irritate the eyes, skin, nose, throat and lungs of individuals, whether or not they are allergic to mold. Other symptoms include nasal and sinus congestion, burning, watery and red eyes, a sore throat, a dry cough, and skin irritation.

These and other symptoms may be associated with exposure to mold. But all of these symptoms may be caused by other exposures or conditions unrelated to mold growth. Therefore, it is important not to assume that mold is the cause of such symptoms.

The effects of mold exposure can be acute or chronic. An acute effect is an immediate, severe reaction to a large exposure. A chronic effect may take days, months or years to manifest, and usually comes from small, repeated exposures.

If a person experiences these symptoms only when occupying a particular building, then that person may possibly be experiencing symptoms of mold exposure.

There are four important indoor allergenic molds. They are Penicillium, Aspergillus, Cladosporium and Alternaria. Alternaria and Cladosporium are outdoor molds that can be found indoors if the doors or windows of a building are left open and the spores are carried in on air currents.

For more detailed information on mold and its health effects, consult a healthcare professional or the state or local health department.

Certified mold inspectors should not offer medical advice to clients. People with health problems that may be related to mold should seek a physician trained in occupational, environmental or allergy medicine. Recommend that clients may wish to consult with a healthcare provider regarding any health problems they might be experiencing


Only a small group of fungi has been associated with infectious disease. Aspergillosis is an infectious disease that can occur in immune-suppressed persons. Health effects in this population can be severe. Several species of Aspergillus are known to cause aspergillosis. The most common is Aspergillus fumigatus. But exposure to this common mold, even to high concentrations, is unlikely to cause infection in a healthy person.

Breathing in mold may also cause hypersensitivity pneumonitis, an uncommon disease that resembles bacterial pneumonia. In addition, mold exposure may result in opportunistic infections in persons whose immune systems are weakened or suppressed.

There are fungal infections that can affect healthy people. There are pathogenic fungi sometimes found inside a building, such as: Blastomyces (which inhabit decaying wood); Coccidioides (found in the southwestern United States); Cryptococcus (found in bird droppings); and Histoplasma (found in bat guano or droppings). People without adequate personal protection equipment (PPE) who come in contact with bird or bat droppings, such as may be found in attics, could be at very high risk. People with compromised immune systems can be seriously affected by fungal infections.

Exposure to fungi associated with bird and bat droppings (Histoplasma capsulatum and Cryptococcus neoformans) can lead to negative health effects in healthy individuals, usually in the form of transient flu-like illnesses. Severe health effects are primarily encountered in immune-compromised persons. People with chronic lung illnesses, such as obstructive lung disease, may develop mold infections in their lungs.


As molds grow under some conditions, some (but not all) of them may produce potentially toxic byproducts called mycotoxins. Mycotoxins are fungal metabolites that have been identified as toxic agents. Some of these mycotoxin-producing molds are commonly found in moisture-damaged buildings. Exposure to mycotoxins can occur from inhalation, ingestion and skin contact. More than 200 mycotoxins from common molds have been identified, and many more remain to be identified. The amount and types of mycotoxins produced by a particular mold depends on many environmental and genetic factors.

No one can tell whether a mold is producing mycotoxins just by looking at it.

Many fungi, including species of Aspergillus, Penicillium, Fusarium, Trichoderma, Memnoniella and Stachybotrys chartarum, can produce potent mycotoxins, some of which are identical to the compounds produced by Stachybotrys chartarum.

There are studies that suggest an association between Stachybotrys chartarum and pulmonary hemorrhage/hemosiderosis in infants, generally those under 6 months old.

Mycotoxins can enter the human body through inhalation, ingestion or skin absorption. The effects of the toxic substance depend on the chemical or the material, the concentration, the route of entry, and the duration of exposure.

Smoking, alcohol, medication, gender, and existing health problems are all potential factors that can influence the effects of a toxic substance entering a body.

Some mycotoxins are known to affect people, but for many mycotoxins, little health information is available. Research on mycotoxins is ongoing.


Mold inspectors and mold remediators can be at risk of developing Organic Dust Toxic Syndrome (ODTS) or Hypersensitivity Pneumonitis (HP). ODTS may manifest itself with flu-like symptoms after a single, heavy exposure to dust contaminated with fungi. It differs from HP in that it is not an immune-mediated disease and does not require repeated exposures to the same causative agent. A variety of biological agents may cause ODTS, including common species of fungi. HP may occur after repeated exposure to an allergen and can result in permanent lung damage.


There have been reports linking negative health effects in office workers to offices contaminated with moldy surfaces, as well as symptoms in residents of homes contaminated with fungal growth.

Fatigue, respiratory ailments, and eye irritation were typically observed in these cases. Occupants and workers inside buildings can reduce their exposure by proper use of personal protective equipment (PPE), including respirators (minimum N-95), gloves, protective clothing, and goggles. Personal hygiene and habits are important for reducing exposure for remediation workers.


Although mold is frequently found in damp buildings, it is not the only potential contaminant. Biological contaminants other than mold, and non-biological contaminants, as well, are often present and may also cause negative health effects. Damp buildings may attract rodents and other pests. Damp or wet building components and furnishings may release chemicals indoors.

Potential contaminants in damp and wet buildings include bacteria, dust mites, cockroaches, and other pests, as well as chemicals emitted by damp building materials and furnishings.