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Mold, dust mites, fungi, spores, and pollen: Bioaerosols in the human environment What are bioaerosols?
A healthy indoor environment is important to you and your family. This includes keeping the air free of biological contaminants, which can cause health problems. Scientists call these airborne contaminants bioaerosols.
Bioaerosols are extremely small living organisms or fragments of living things suspended in the air. Dust mites, molds, fungi, spores, pollen, bacteria, viruses, amoebas, fragments of plant materials, and human and pet dander (skin which has been shed) are some examples. They cannot be seen without a magnifying glass or microscope.
Can bioaerosols cause health problems?
They can cause severe health problems. Some, like viruses and bacteria, cause infections (like a cold or pneumonia). Others cause allergies. Both allergic responses and infections may be serious or even fatal.
An allergic reaction occurs when a substance provokes formation of antibodies in a susceptible person. We call substances which will cause an allergic reaction in some people antigens or allergens. Bioaerosols may cause allergic reactions on the skin or in the respiratory tract. Rashes, hay fever, asthma (tightness in the chest, difficulty in breathing), and runny noses are common allergic reactions.
A few people develop a severe allergic reaction in the lung, which can destroy lung tissue. This is called hypersensitivity pneumonitis. It is not an infection, but repeated episodes can lead to infections of the lung, such as bacterial pneumonia.
Hypersensitivity pneumonitis can be triggered by exposure to very small amounts of the allergen, once a person is sensitive to it. Symptoms can range from tightness in the chest, cough, and difficulty in breathing, to low-grade fever, muscle aches, and headaches.
What are sources of bioaerosols in the home?
Molds, mildews, bacteria, and dust mites like the same conditions that we do--warmth and moderate to high humidity. They need little more than a constant moisture supply for survival. You may find bacteria, molds, and mildews in air conditioning equipment, humidifier reservoirs, dehumidifier drip pans, shower heads, toilets, and ice machines. Water damaged carpets, ceiling panels, walls, and paneling are prime sites for new growth if they are allowed to stay damp. When molds, mildew, dust mites, and bacteria are disrupted or release their spores into the air, this results in bioaerosol formation.
Molds and mildews develop from spores, which are in the air all around you. As soon as spores settle in an area with the right conditions for growth, they establish colonies, which are often visible to the naked eye. These colonies are a source of more spores, can cause unsightly stains, and may release low levels of toxic chemicals called mycotoxins into the air.
Humidifiers are such a common source of bioaeorsols that cause health problems that doctors now use the term humidifier fever. Protozoa, amoebas, and strains of bacteria have been found in humidifiers, and these are readily released into the air with the moisture produced by humidifiers. These have ben linked to allergic responses in sensitive people.
Mold and mildew may be found in the ductwork of your heating or cooling systems. If there are leaks in the ductwork, or places where moisture and outside air get into the system, mold and mildew can grow. Sometimes they are found in the coils of an air conditioner or in the connection between the unit and the ductwork. Moisture problems are worse where ductwork insulation is on the inside as opposed to the outside of the duct. The insulation's porous surface collects dust and moisture. Mold and mildew may also grow on dirty furnace and air conditioning filters. Plumbing leaks and dampness in attics, basements, and crawl spaces can increase humidity inside your home and promote the growth of agents that will be released as bioaerosols. Bathrooms without outside-vented exhaust fans, combustion appliances like kerosene space heaters, drying laundry indoors, and venting clothes dryers to attics or crawl spaces can also increase the humidity levels in your home.
Dust mites and their waste products are the most common allergens in indoor air. Dust mites eat human and pet skin (dander) as it is shed. It has been estimated that we shed about seven million cells per minute! Dust mites live in rugs and carpets, sheets, mattresses and pillows, and upholstered furniture. Ten to 15 percent of people are allergic to dust mites. Of the people who have other allergies, 40 percent are also allergic to dust mites.
What measures can be taken to control bioaerosols in the home?
First, lower the relative humidity in your home, basement or crawl space, and attic. Relative humidity is the amount of moisture in the air at a given temperature. You may want to see Identifying and Correcting Moisture Problems in Homes. The humidity fluctuates in your home, depending on:
How warm or cool the air is indoors. How many moisture-producing activities (drying clothes indoors, showers) are taking place. Whether there is a constant source of moisture (leaks, damp foundations and attics). How much moisture is being vented to the outside.
If you can keep relative humidity below 50 percent, you can reduce problems with dust mites, mold, and mildew. A hygrometer can be used to measure indoor humidity levels. You can buy a hygrometer from some nursery or garden stores, and from hardware stores.
There is little medical research supporting the use of a humidifier, so try to avoid using one. If your home is extremely dry and you must use a humidifier, a steam vaporizer or warm mist humidifier causes fewer problems. Do not humidify indoor air to a relative humidity level higher than 50 percent.
Ultrasonic and cool mist (impeller-type) humidifiers can send microorganisms from their water tanks into the air. Ultrasonic humidifiers use sound vibrations to create a cool mist. Impeller humidifiers create a cool mist by means of a high-speed rotating disk. If you do use a humidifier:
Empty the tank, wipe all surfaces dry, and refill the water in portable humidifiers each day. Clean portable humidifiers every third day. Unplug the humidifier before cleaning and follow the manufacturer's recommendations on the use of cleaning agents or disinfectants.
If you have no specific instructions on cleaning your humidifier, use a 3 percent solution of hydrogen peroxide. Never use the humidifier with any of the cleaning agent or disinfectant in the tank. Rinse the tank thoroughly several times with tap water to keep cleaning or disinfecting chemicals out of the air.
