Are you worried about the air you breathe? Feeling fine everywhere except at home, or feeling worse the longer you stay inside, is common enough that health agencies have a name for it: sick building syndrome. The U.S. Environmental Protection Agency says the air in homes and other buildings can be more seriously polluted than the air outside.

Studies from the United States and Europe show that people in industrialized nations spend more than 90 percent of their time indoors, and infants, older adults, and people with chronic illness usually spend even more. Because so many pollutants build up indoors rather than outdoors, an unexplained headache, cough, or bout of dizziness is worth asking about your house before you ask about anything else.

The trouble is that many of these symptoms overlap. A stuffy nose, fatigue, and nausea can point to a dozen different causes, and etiology can be difficult to establish because the signs are so nonspecific. What follows is a breakdown of the most common indoor air hazards, the symptoms tied to each one, and what tends to give a problem away before you call anyone in.

Common Indoor Air Hazards

Most indoor air pollution comes from the accumulation of contaminants from sources inside the home combined with poor ventilation. Weatherizing a home, adding insulation and caulking to save on energy costs, reduces air circulation and traps those contaminants inside instead of letting outdoor air dilute them. That combination of tighter construction and recirculated air is a large part of why indoor air problems have increased even as homes have gotten more efficient.

Carbon monoxide

Carbon monoxide is an odorless, colorless gas released from fuel burning stoves, heaters, furnaces, and other appliances that are not properly vented. It blocks the movement of oxygen in the body, and depending on how much is breathed in, it can cause extreme tiredness, headache, confusion, nausea, dizziness, and a fast heart rate. Very high levels can cause death. Older adults, infants, pregnant people, and anyone with heart or lung disease are especially sensitive to it. Because the early symptoms mimic the flu, it is worth suspecting carbon monoxide when an entire household develops the same symptoms at the start of the heating season and they do not resolve with time.

Nitrogen dioxide and sulfur dioxide

Both gases come mainly from combustion, natural gas and kerosene for nitrogen dioxide, burning kerosene in space heaters for sulfur dioxide, and both act as irritants to the eyes, nose, throat, and respiratory tract. Nitrogen dioxide can cause shortness of breath at high concentrations and, over time, contribute to chronic bronchitis. Sulfur dioxide is extremely irritating to the eyes and upper respiratory tract even at low concentrations, and some people with asthma react to it with tightened airways after only a brief exposure.

Formaldehyde and other volatile organic compounds

Volatile organic compounds are emitted as gases from paints, finishes, cleaners, pesticides, adhesives, and new furniture, and formaldehyde is one of the most common. It comes from resins used in plywood, paneling, fiberboard, and particleboard, and from permanent press fabric and mattress ticking. It irritates the eyes, nose, and throat, and can cause a burning or tingling sensation, chest tightness, wheezing, headache, dizziness, and nausea. It has also been classified as a probable human carcinogen. New carpet is a source too, since it emits volatile organic compounds along with the adhesives and padding used to install it, and people commonly report eye, nose, and throat irritation, headaches, skin irritation, coughing, and fatigue after new carpet goes in.

Radon

Radon does not cause any symptoms you would notice. It is a naturally occurring radioactive gas, odorless, colorless, and tasteless, that seeps up from uranium decaying in the soil and rock under a home and enters through cracks in the foundation, floor drains, and sumps. It is the second leading cause of lung cancer after smoking, and smokers exposed to elevated radon face a much higher risk than nonsmokers exposed to the same levels. Because there is nothing to feel, testing is the only way to know if a home has a radon problem.

Secondhand smoke

Tobacco smoke contains thousands of compounds, including formaldehyde and carbon monoxide, and exposure to it in adults is linked to a runny or stuffy nose, a persistent cough, irritated eyes, headache, wheezing, and flareups of existing respiratory conditions. Children are more sensitive to it than adults. Exposure in infants and children up to age three roughly doubles the rate of pneumonia, bronchitis, and bronchiolitis, and it is linked to asthma onset and to worse asthma symptoms.

Mold, dust mites, and other biological agents

Biological pollutants, mold, mildew, bacteria, viruses, dust mites, and pet dander, thrive where relative humidity stays above 50 percent, where there has been flooding or a leak, or where a humidifier, dehumidifier, or air conditioner is not kept clean. They cause allergic reactions ranging from sneezing, watery eyes, and a stuffy nose to asthma, as well as coughing, dizziness, fever, lethargy, shortness of breath, and digestive problems. A poorly maintained humidifier can also cause humidifier fever, a flu like illness marked by fever, headache, chills, and muscle aches that normally clears up within a day once the exposure stops.

Lead

Lead dust mostly comes from paint in homes built before the material was restricted, especially when old paint is disturbed by sanding, scraping, or renovation. In adults, exposure is linked to stomach discomfort, fatigue, personality changes, headache, hearing loss, and tremor. In infants and small children, who are more vulnerable, it can cause irritability, abdominal pain, loss of coordination, seizures, learning problems, and hyperactivity.

Asbestos

Asbestos does not cause symptoms on its own, and intact material that is not disturbed generally does not pose a risk. It shows up in older homes in pipe and furnace insulation, floor tiles, ceiling tiles and panels, and some textured paints. Cutting, sanding, or otherwise disturbing these materials can release fibers into the air, and breathing them in over years is linked to lung cancer, asbestosis, and mesothelioma. Smoking on top of asbestos exposure raises the lung cancer risk far more than either one alone.

Other Indoor Pollutants

These are other common household air pollutants worth ruling out:

Signs Something Is Wrong With Your Air

Beyond how you feel, the home itself often gives off its own warning signs:

How To Lower Your Risk

In general:

Bathroom

Bedroom

Kitchen

Garage

Laundry and utility areas

If a symptom keeps coming back whenever you are home and eases up whenever you leave, mention it to your doctor and consider testing for the specific hazard it points to before assuming the worst. Your state or local health department can also talk through the symptoms and possible causes with you directly.