Is poor indoor air quality making you sick?

Indoor air quality isn't on most people's radar. Only 9 percent of Americans consider it a threat to their health, and 70 percent aren't concerned about it at all, according to a recent survey by the Consumer Reports National Research Center. But many of the things people do—or don't do—can add to the stew of airborne contaminants in their homes and worsen asthma, allergies, and other health conditions.

Almost half of Americans use air fresheners at least once a week, and 34 percent use candles or incense that frequently, our nationally representative survey found. Roughly 40 percent rarely or never clean their humidifier or kitchen range hood, though they use it daily. One quarter have never cleaned or replaced their furnace filter. And almost 20 percent still smoke at home or let others smoke there. All of those things can worsen indoor air quality.

Many problems are easy to fix—or avoid. Here's our advice on how to protect your family and home.

Carbon monoxide and radon are colorless, odorless, and deadly. CO kills quickly. Faulty gas ranges, cooktops, and furnaces can emit CO, as can wood, kerosene, and propane heaters. Gas generators also emit CO, so don't run them in a garage or outside near open windows.

Radon is the top cause of lung cancer among nonsmokers, though it can take years of exposure. It seeps from rocks, soil, or water beneath your house. Radon levels can vary greatly, even from home to home on the same block. The only way to know whether your house has a radon problem is to test for it.

What you can do

• Have your heating system and any other fuel-burning appliance inspected annually.
•  Install a CO alarm on each level, including the basement.
• Change the batteries on your CO alarm according to your owner's manual, or at least every year. Only 53 percent of those we surveyed said they did that.
• Replace your CO alarm every five years.
• Run a long-term (90-day or longer) radon test. They cost $20 to $40 and are sold online. If your home has 2 to 4 picocuries per liter (pCi/L) of radon or higher, consider treatment ($800 to $2,500).

Even vented gas ranges, cooktops, furnaces, and fireplaces can release harmful gases, soot, and particles into the air if they're not properly installed and maintained. The same is true with vented wood-burning stoves and fireplaces. Unvented fuel-burning appliances always release small amounts of those substances.

When someone in your household smokes, the nicotine released by the cigarettes or cigars adheres to walls, carpeting, drapes, and other indoor surfaces and can react with nitrous acid (chiefly from unvented gas appliances) to form carcinogens, according to a recent Department of Energy study.

What you can do

• Always run the exhaust hood when using your gas range or cleaning your oven, or open a window.
• Periodically inspect burner ports on your gas stove and clean clogged ones with a needle.
• Clean a frequently used chimney annually.
• Ban smoking from your house.

A 2009 study by the Environmental Working Group identified 457 air contaminants—24 linked to serious health concerns, including cancer—in 21 household cleaners. Products labeled "green" were better overall, though the group found 93 contaminants in Simple Green Concentrated Cleaner.

That's partly because many claims on cleaning products aren't based on any standards. Products with the Design for the Environment (DfE) label from the Environmental Protection Agency have been screened by a third party and contain relatively safe ingredients.

Fragrances in cleaners are seldom disclosed. Many manufacturers list product ingredients on their websites, but they don't have to list fragrance ingredients. And one fragrance can contain 50 to 200 compounds, including dozens of volatile organic compounds. Terpenes, for example, give products a pine or lemon scent, but they're linked to respiratory problems. They also can react with ambient ozone to form formaldehyde, a known carcinogen, and other irritants. But William Troy, Ph.D., a former chairman of the International Fragrance Association North America, says people need to consider exposure levels. "Fragrance exposure via cleaners is low," he says, "and does not present a hazard to the consumer."

What you can do

• Though it sounds obvious, always read product labels and follow directions for use. And open a window or run a fan when cleaning.
•  If you have asthma or allergies, use products without fragrances or those with the DfE label.
• For a homemade glass cleaner, mix 1 tablespoon of vinegar or lemon juice with 1 quart of water. To clean toilets, use baking soda or vinegar and a toilet brush. To help get rid of odors, sprinkle baking soda on rugs or carpets, wait 15 minutes, then vacuum.

Behind the soothing fragrances of air fresheners, candles, and incense are volatile organic compounds. Air fresheners can also contain phthalates, which are linked to cancer and reproductive problems.

"A few manufacturers changed their products after our 2007 report found phthalates in 12 of 14 air fresheners we tested," says Gina Solomon, M.D., a senior scientist at the Natural Resources Defense Council. "That's good, because companies are reformulating to make their products safer, but it's also bad because it's hard to know what's currently in any given product."

Scented candles and incense also release soot and particles into the air, which can trigger asthma attacks and allergic reactions.

"Most patients who stop using scented products have noticed an improvement in their symptoms," says Stanley Fineman, M.D., president of the American College of Allergy, Asthma and Immunology.

What you can do

• If you or someone in your household has serious allergies or asthma, avoid air fresheners, candles, and incense.
• If pollen or related allergies keep you from opening windows, run your air conditioner or forced-air cooling system with a clean filter. Or consider a filter-based air purifier. (See our air purifiers buying guide.)

The ideal indoor relative humidity is between 30 to 50 percent. Less than that and nasal passages can become dry. At higher levels mold can grow. Humidifiers and dehumidifiers can help or create more problems.

Humidifiers should be emptied daily and disinfected regularly because mold can grow within 24 to 48 hours on wet surfaces. Mold and bacteria in the tank can be released into the air. Dehumidifier filters and tanks also need maintenance, though not as much. Check the manufacturer's directions.

Bathroom exhaust fans also reduce humidity but need cleaning to avoid dust buildup, a medium for germs.

Not all cleaning is smart. Air ducts need cleaning only in limited circumstances—when there's visible mold, pests, or dust clogging them. Still, 49 percent of survey respondents clean their ducts at least once a year.

What you can do

• Every season, check gutters, leaders, and downspouts for proper pitch, clogs, and broken fasteners or connections.
• Make sure that gutter pipes extend at least 5 feet from the house and that the soil around the foundation slopes away from the house.
• Avoid mold test kits; we've found them to be unreliable.
• Treat small areas of mold with a mixture of 1 part chlorine bleach and 16 parts water. Wear goggles, an N-95 respirator, and heavy-duty gloves. Make sure to ventilate the room when you're working

Planning to paint? Old lead-based paint is the most significant source of lead poisoning in the U.S. Roughly 35 million homes, or about half of those built before lead-based paint was banned in 1978, have lead paint, according to a recent federal study. Yet only 17 percent of those we surveyed said they had their homes checked for it.

You can put yourself in danger by scraping, sanding, or burning lead-based paint. Lead can also be released when painted surfaces rub against each other, as when a window is opened. Children are particularly at risk.

What you can do

• If you have young children and an older home, have it tested for lead by an EPA- or state-certified pro using an XRF machine, or have paint-chip analysis by an EPA-certified lab.
• Mop floors and wipe windows and surfaces that children might chew on, such as crib rails.
• Leave lead-based paint undisturbed if it's in good condition, except where painted surfaces rub against each other. For damaged areas, follow the EPA's guidelines for removing lead paint or hire a painter who is EPA-certified.