The EPA considers bacteria, molds, mildew, viruses, animal dander, cat saliva, house dust, mites, cockroaches and pollen all biological contaminants. Excessive moisture creates breeding grounds for these contaminants, so ventilate adequately and keep relative humidity between 30 percent and 50 percent to prevent condensation on building materials.

Regular household cleaning and maintenance go a long way toward limiting exposure. Change filters and have heating and cooling equipment cleaned and checked regularly by a professional; these systems can become not only breeding grounds for mold and other biological contaminants but also superhighways for dispersing them throughout the home.

If these methods don’t suffice, an indoor air-cleaning device may help an affected area. However, avoid ozone generators that are sold as air cleaners. The EPA warns: “Whether in its pure form or mixed with other chemicals, ozone can be harmful to health.”

Basements can be a particular trouble zone. The EPA recommends you clean and disinfect basement drains regularly and that you not finish a basement unless all moisture issues are abated.

No one knows exactly how many homes have mold behind the walls, but the best current estimate is about 70 percent, according to Ronald E. Gots, M.D., Ph.D., of the International Center for Toxicology and Medicine. The EPA and World Health Organization state that some molds have the potential to cause health problems, particularly allergic reactions and asthma, in people who are susceptible.

To get rid of mold, scrub surfaces with detergent, preferably a water-based, VOC-free product like Microbloc dsinfx as opposed to bleach. Replace porous materials such as ceiling tile and carpet with non-porous or mold-resistant ones. If the mold damage covers more than 10 square feet, the EPA recommends hiring a professional.

Most important: Fix the underlying issue. “Mold is not the problem. It’s an indicator of a moisture problem,” says Kurt Salomon, president of the American Society of Home Inspectors. “You can get rid of the mold but if you don’t address the leaky pipes, high humidity and water intrusion, the mold will come back.”

To cut down on household dust, declutter, reduce paper, eliminate smoking and regularly change or clean the furnace and air conditioner filters. Also, park your shoes at the door — two-thirds of all dust contaminants are tracked into the home from the outside.

To minimize the amount of dust kicked up during cleaning — especially if you are concerned about lead dust — wipe down floors with a damp mop, dust with a damp cloth and clean surfaces with a vacuum cleaner with a HEPA filter.

You probably don’t need to have your air ducts cleaned unless there is mold growing inside, they are infested with vermin or they are excessively clogged with debris. Duct cleaning costs between $400 and $1,000. The National Air Duct Cleaners Association cautions consumers against air duct cleaning companies that make sweeping claims about health benefits of their services and/or are not upfront about fees.

Even when present in very low, hard-to-measure concentrations, semi-volatile organic compounds (SVOCs) pose serious health risks — organ and nervous system damage and cancer included.

SVOCs are hard to avoid, as they are ubiquitous in our homes. Phthalate esters are colorless, odorless and used to make plastics soft and flexible, such as polyvinyl chloride (PVC). Polybrominated diphenyl ethers (PBDEs) have been widely used as flame retardants in furniture cushions, textiles, plastics, paints and electronic appliances. Naphthalene is the key ingredient in mothballs. Other man-made chemicals such as the dry-cleaning solvent known as PERC (perchloroethylene) and the blue, sweet-smelling liquid called TCE (trichloroethylene) that is found in spot removers and carpet-cleaning fluids are toxic to the brain and nervous system, and they are likely carcinogens.

You can minimize exposure in the home by using green cleaning methods. To protect woolens from pests, wash items and let them dry in the sun (which also helps get rid of mothball odor) before storing them with cedar chip sachets. Read labels before purchasing and avoid buying items that contain phthalates and PBDEs.

Thousands of household products — paints, paint-strippers, adhesives, MDF, carpet, glues, cleaners, fuels, degreasers and more — off-gas volatile organic compounds. These chemicals cause a number of health effects including eye, nose and throat irritation; headache; nausea; liver, kidney and central nervous system damage; and cancer.

According to the EPA, studies have found that VOC levels are two to five times higher indoors than outdoors. During and for several hours immediately after certain activities, such as paint-stripping, levels may be 1,000 times background outdoor levels.

There are many steps to reduce exposure. For example, replace vinyl wallcoverings with Cradle-to-Cradle-certified ones made with new polymers and water-based inks and coatings. If dry-cleaned goods have a strong chemical odor, which indicates a high concentration of the solvent PERC (perchloroethylene), do not accept them until they have been properly dried. Use non- or low-VOC paints, glues, epoxies, adhesives and building products. Even when using low-VOC products, ventilate the space with plenty of fresh air. Dispose of even small amounts you won’t use right away in an environmentally responsible way.

Exposure to low concentrations of formaldehyde may cause eye, nose or throat irritation, rashes, breathing problems, nausea, asthma attacks and allergic reactions. And formaldehyde causes cancer in animals and humans.

The American Lung Association recommends you use furniture and pressed-wood board made with laminated surfaces because they release less formaldehyde. Allow plywood and other formaldehyde-containing materials to air out before you use them indoors. If possible, use non-toxic alternatives to formaldehyde-containing products like glue and adhesives. Ventilation is key, so open windows and use exhaust fans to bring in a fresh supply of air. Also, wash permanent-press clothing before wearing. Formaldehyde is used in the production of special fabrics.

You can’t see, taste or smell carbon monoxide (CO), a toxic gas produced by incomplete combustion of fuel-burning devices, and people often dismiss the symptoms of CO poisoning (headache, nausea, dizziness and confusion), which can be fatal. This “silent killer” accounts for an estimated 15,000 emergency room visits and 500 deaths a year.

“Carbon monoxide is an underappreciated risk, particularly during heating season when people don’t open windows as much to let in fresh air,” says Meri-K Appy of Safe Kids USA. “But there’s no other way to know you’ve got a problem unless you have a CO detector to let you know levels have reached a dangerous level.” If the detector sounds, evacuate your home immediately and call 911. And be sure to replace the battery when you change the time on your clocks each spring and fall.

According to the Chimney Safety Institute of America, the chimneys and connector pipes that serve oil and gas furnaces are subject to weathering, animal invasions, deterioration/rust-out and the accumulation of nest materials and debris. As a safeguard, have fuel-burning furnaces, stoves and fireplaces — as well as their connections and exhaust vents — inspected and serviced before each heating season. And never idle your car in the garage.

Lead poisoning is the leading environmentally induced illness in children, according to OSHA. If you live in a home built before 1978, chances are it contains lead paint.

To protect you and your family, make sure there is no peeling or chipped paint. You can encapsulate lead paint by painting over it. If you must scrape or sand lead paint, wear a HEPA respirator, enclose the workspace with plastic, keep debris contained and “work wet” to minimize dust. Clean up with a HEPA filter vacuum and damp mop, and be careful not to track lead dust through the house.

Because it can be “tough for DIYers to follow all best practices,” Rebecca Morley, president of the National Center for Healthy Housing, recommends hiring a contractor certified in lead abatement. A new EPA regulation requires anyone working in homes built before 1978 to take an eight-hour lead safety certification course or risk a $32,000 fine. More than 500,000 contractors have been certified since April 2010, but it’s up to the homeowner to ask for proof of certification.

To find a lead sampling technician to do a dust test, including the soil around your house (a common source of lead), call the EPA’s lead hot line at 800-424-LEAD.

Radon is a naturally occurring radioactive gas, which cannot be seen, smelled or tasted but is found in the dirt and rocks beneath houses, in well water and in some building materials. When you breathe radon, the sensitive cells in your airway get irritated, increasing the risk of lung cancer. Radon causes an estimated 20,000 lung cancer deaths each year, but it can take up to 20 years of exposure before one falls ill.

The U.S. Surgeon General and EPA recommend that all homes be tested for radon; even if the house next door to you tests low, your particular house could be at risk. Short-term tests take two days (often for real estate transactions), while long-term tests take about 90 days but give more accurate results.

If your house tests above EPA standards, a remediation professional can retrofit an exhaust vent from a suction pit underneath the foundation slab to the outside of the house. Costs range from $800 to $2,500. For more information, contact the EPA’s radon hot line at 800-55RADON (557-2366).

Before 1985, asbestos was used in more than 3,000 construction products, from flooring and insulation to soundproofing for strength and flame-resistance. The government outlawed asbestos after it was discovered that the mineral fiber causes lung cancer and mesothelioma.

If you live in a home that contains mid-century vinyl floor tile, ceiling tiles or insulation, have a professional asbestos inspector test your home before you do any remodeling. Unless there is a need to remove or disturb the material, which would release asbestos fibers into the air, leave it alone.

In many cases, says the Resilient Floor Covering Institute, new flooring can be successfully installed over the existing. For material containing 1 percent asbestos that is friable — so damaged that it crumbles in your hand — it’s best to hire government-certified asbestos contractors to remove or encapsulate it.

The National Fire Protection Association reports that of the 2,565 civilian deaths from home fires in 2009, almost two-thirds (63 percent) involved homes with non-working or non-existent smoke alarms. New code requires smoke alarms in every room, bedrooms being of most importance.

“If you have a fire, you need to know about it,” says Meri-K Appy, president of Safe Kids USA, who recommends having hard-wired, interconnected smoke alarms, “so that if fire breaks out in the basement and you’re two floors up sleeping, at the first moment the basement alarm goes off, all will go off.” Such alarms buy you precious time; it can take fewer than three minutes from the time a fire starts to the time of “flashover” – complete ignition of all gasses and combustible elements in a room.

She also notes that smoke alarms should be replaced every 10 years. That’s a good time to upgrade to either a hard-wired or wireless interconnected system. New technologies include ionization systems that react to fast-burning fires, photo-electric alarms that react quickly to smoldering fires, integrated carbon monoxide detectors and fire sprinklers, remote controls and smart-phone apps.

The National Fire Protection Association reports that of the 2,565 civilian deaths from home fires in 2009, almost two-thirds (63 percent) involved homes with non-working or non-existent smoke alarms. New code requires smoke alarms in every room, bedrooms being of most importance.

“If you have a fire, you need to know about it,” says Meri-K Appy, president of Safe Kids USA, who recommends having hard-wired, interconnected smoke alarms, “so that if fire breaks out in the basement and you’re two floors up sleeping, at the first moment the basement alarm goes off, all will go off.” Such alarms buy you precious time; it can take fewer than three minutes from the time a fire starts to the time of “flashover” – complete ignition of all gasses and combustible elements in a room.

She also notes that smoke alarms should be replaced every 10 years. That’s a good time to upgrade to either a hard-wired or wireless interconnected system. New technologies include ionization systems that react to fast-burning fires, photo-electric alarms that react quickly to smoldering fires, integrated carbon monoxide detectors and fire sprinklers, remote controls and smart-phone apps.

According to the Consumer Product Safety Commission, GFCIs have contributed “significantly” to the reduction of electrocution and severe electric shock incidents since their introduction in the early 1970s. The National Electrical Code requires GFCIs, an inexpensive device, for receptacles with proximity to water: outdoors, bathrooms, garages, kitchens, crawlspaces and unfinished basements, laundry/utility rooms, and pools and spas.

You should also take commonsense precautions when it comes to electricity. All electrical outlets and switches should be covered by faceplates. Use the right light bulbs in all lamps and lights. Check the wattage requirements by looking inside the fixture.

Only use household appliances in good working condition. All electrical appliances, cords and tools should be listed by a nationally recognized, independent testing laboratory, such as UL or ETL. Periodically check the Consumer Product Safety Commission’s list of product recalls to see if any of your appliances have been recalled for fire hazard or other issues.

Even a little clutter underfoot can be hazardous to your health, especially on stairs and in dark hallways. To prevent trips and falls, keep those areas clear and get rid of slippery scatter rugs.

“Lighting is also a big factor in falls,” says Meri-K Appy, president of Safe Kids USA, who recommends having lights at the top and the bottom of stairs. Also, don’t delay repairing loose treads and rails.

In the bathroom, grab bars in the bath or shower are a good idea for any age. Make sure throw rugs have rubberized mats or bottoms — in the bathroom and throughout the house.

The same rules apply outside. In the yard, shore up loose pavers and crumbling pavement, and make sure pathways and entrances are well lit.

As if vermin were not repellent enough, here’s a fun fact: When urine from rats and mice dries, proteins can become airborne and become potent allergens.

The Surgeon General and EPA advocate Integrated Pest Management (IPM), which uses commonsense strategies to reduce sources of food, water and shelter for pests and, when necessary, the judicious careful use of pesticides.

The US Green Building Council recommends a number of nontoxic strategies for keeping pests out of your home without endangering your health or the environment. These include planting landscaping at least 24 inches from the home, treating lumber and cellulose material with borates and sealing all cracks, joints and other entry points with fiber cement board or galvanized insect screen.

Avoid using mothballs, which contain carcinogens naphthalene and paradichlorobenzene. If you do use pesticides, mix or dilute the ingredients outdoors, and ventilate affected indoor areas well.