Outdoor air pollution in cities is a major health problem. Much effort and money continue to be spent cleaning up pollution in the outdoor air. But air pollution can be a problem where you least expect it, in the place you may have thought was safest — your home. Many ordinary activities, such as cooking, heating, cooling, cleaning, and redecorating, can cause the release and spread of indoor pollutants at home. Studies have shown that the air in our homes can be even more polluted than outdoor air. Many Americans spend up to 90% of their time indoors, often at home. Therefore, breathing clean indoor air can have an important impact on health. People who are inside a great deal may be at greater risk of developing health problems or having problems made worse by indoor air pollutants. These people include infants, young children, the elderly, and those with chronic illnesses. Many factors determine whether pollutants in your home will affect your health. They include the presence, use, and condition of pollutant sources, the level of pollutants both indoors and out, the amount of ventilation in your home, and your overall health.

Biological pollutants are or were living organisms. They promote poor indoor air quality and maybe a major cause of days lost from work and school, and of doctor and hospital visits. Some can even damage surfaces inside and outside your house. Biological pollutants can travel through the air and are often invisible. Some common indoor biological pollutants are:

• animal dander (minute scales from hair, feathers, or skin);
• dust mite and cockroach parts;
• infectious agents (bacteria and viruses); and
• pollen.

Some of these substances are in every home. It is impossible to get rid of them all. Even a spotless home may permit the growth of biological pollutants. Two conditions are essential to support biological growth:  nutrients and moisture. These conditions can be found in many locations, such as bathrooms, damp or flooded basements, wet appliances (such as humidifiers and air conditioners), and even some carpets and furniture. Modern materials and construction techniques may reduce the amount of outside air brought into buildings, which may result in high moisture levels inside. Using humidifiers, unvented heaters, and air conditioners in our homes have increased the chances of moisture forming on interior surfaces. This encourages the growth of certain biological pollutants.

Most information about sources and health effects of biological pollutants is based on studies of large office buildings and surveys of homes in the northern U.S. and Canada. These surveys show that 30% to 50% of all structures have damp conditions which may encourage the growth and buildup of biological pollutants. This percentage is likely to be higher in warm, moist climates. Some diseases and illnesses have been linked with biological pollutants in the indoor environment. However, many of them also have causes unrelated to the indoor environment. Therefore, we do not know how many health problems relate only to poor indoor air.

All of us are exposed to biological pollutants. However, the effects on our health depend on the type and amount of biological pollution and the individual person. Some people do not experience health reactions from certain biological pollutants, while others may experience one or more of the following reactions:

• allergic;
• infectious; and/or
• toxic.

Except for the spread of infections indoors, allergic reactions may be the most common health problem with indoor air quality in homes. They are often connected with animal dander (mostly from cats and dogs), with house dust mites (microscopic animals living in household dust), and with pollen. Allergic reactions can range from mildly uncomfortable to life-threatening, as in a severe asthma attack. Some common signs and symptoms are:

• watery eyes;
• runny nose and sneezing;
• nasal congestion;
• itching;
• coughing;
• wheezing and difficulty breathing;
• headache; and
• fatigue.

Health experts are especially concerned about people with asthma. These people have very sensitive airways that can react to various irritants, making breathing difficult. The number of people who have asthma has greatly increased in recent years. The number of people with asthma has gone up by 59% since 1970, to a total of 9.6 million people. Asthma in children under 15 years of age has increased 41% in the same period, to a total of 2.6 million children. The number of deaths from asthma is up by 68% since 1979, to a total of almost 4,400 deaths per year.

Are you concerned about the effects on your health that may be related to biological pollutants in your home? Before you discuss your concerns with your doctor, you should know the answers to the following questions. This information can help the doctor determine whether your health problems may be related to biological pollution.

• Does anyone in the family have frequent headaches, fevers, itchy and watery eyes, a stuffy nose, dry throat, or a cough? Does anyone complain of feeling tired or dizzy all the time? Is anyone wheezing or having difficulties breathing on a regular basis?
• Did these symptoms appear after you moved into a new or different home?
• Do the symptoms disappear when you go to school or the office or go away on a trip, and return when you come back?
• Have you recently remodeled your home or done any energy-conservation work, such as installing insulation, storm windows, or weather stripping? Did your symptoms occur during or after these activities?
• Does your home feel humid? Can you see moisture on the windows or on other surfaces, such as walls and ceilings?
• What is the usual temperature in your home? Is it very hot or cold?
• Have you recently had water damage?
• Is your basement wet or damp?
• Is there any obvious mold or mildew?
• Does any part of your home have a musty or moldy odor?
• Is the air stale?
• Do you have pets?
• Do your house plants show signs of mold?
• Do you have air conditioners or humidifiers that have not been properly cleaned?
• Does your home have cockroaches or rodents?

Infectious diseases caused by bacteria and viruses, such as the flu, measles, chickenpox, and tuberculosis, may be spread indoors. Most infectious diseases pass from person to person through physical contact. Crowded conditions with poor air circulation can promote this spread. Some bacteria and viruses thrive in buildings and circulate through indoor ventilation systems. For example, the bacterium causing Legionnaire’s Disease, a serious and sometimes lethal infection, and Pontiac Fever, a flu-like illness, have circulated in some large buildings.

Toxic reactions are the least studied or understood health problem caused by some biological air pollutants in the home. Toxins can damage a variety of organs and tissues in the body, including the liver, the central nervous system, the digestive tract, and the immune system.

There is no simple or cheap way to sample the air in your home to determine the level of all biological pollutants. Experts suggest that sampling for biological pollutants is not a useful problem-solving tool. Even if you had your home tested, it is almost impossible to know which biological pollutant(s) cause various symptoms or health problems. The amount of most biological substances required to cause disease is unknown and varies from one person to the next. Does this make the problem sound hopeless? On the contrary, you can take several simple, practical actions to help remove sources of biological pollutants, to help get rid of pollutants, and to prevent their return.

Begin by touring your household. Follow your nose, and use your eyes. Two major factors help create conditions for biological pollutants to grow:  nutrients and constant moisture with poor air circulation.

1. Dust and construction materials, such as wood, wallboard, and insulation, contain nutrients that allow biological pollutants to grow. Firewood also is a source of moisture, fungi, and bugs.
2. Appliances, such as humidifiers, kerosene and gas heaters, washers and clothes dryers, dishwashers, and gas stoves, add moisture to the air.

A musty odor, moisture on hard surfaces, and even water stains may be caused by:

• air-conditioning units;
• basements, attics, and crawlspaces;
• bathrooms;
• carpets;
• heating and air-conditioning ducts;
• humidifiers and dehumidifiers; and
• refrigerator drip pans.

What You Can Do About Biological Pollutants

Before you give away the family pet or move, there are less drastic steps you can take to reduce potential problems. Properly cleaning and maintaining your home can help reduce the problem and may avoid interrupting your normal routine. People who have health problems, such as asthma, or who are allergic, may need to do this and more. Discuss this with your doctor.