Home sweet home? Most houses are safe and healthy. But there are a few out there that turn out to be killers. Here is a list of the worst offenders, where they come and what you can do to fight back, followed by a link to more information for each:

1. Radon- Colorless, odorless, tasteless, and chemically inert radioactive gas. Causes Lung Cancer. Smoking, radon, and secondhand smoke are the leading causes of lung cancer. In fact, radon in indoor air is estimated to cause about 21,000 lung cancer deaths each year in the United States.

Source: Formed by the natural radioactive decay of uranium in rock, soil, and water. Naturally existing, low levels of uranium occur widely in Earth's crust. Found in all 50 states. Unless you test for it, there is no way of telling how much is present.

What to Do: Testing with do-it yourself kit- $10 at your local hardware store. If your home tests positive for high levels of radon, there are several effective radon mitigation methods available. Average cost for home radon mitigation: $1,200 See: http://www.nsc.org/issues/radon/

2. Asbestos- Damaged asbestos releases airborne fibers,which become a health hazard. Breathing high levels of asbestos fibers can lead to an increased risk of lung cancer in the form of mesothelioma or asbestosis.

Source: Most commonly found in insulation wrap on water pipes and heating ducts, but also vinyl floor tile backing, floor tile adhesives, asbestos roofing shingles, asbestos insulation (homes built between 1930 and 1950).

What to Do: Take precautions to avoid damaging asbestos materials. If the asbestos is frayed or breaking apart, you need to have either repaired, sealed off, or removed. Hire an accredited professional for the job, do not attempt to do it yourself. See:http://www.epa.gov/asbestos/

3. Toxic Mold- Some species of mold that grow in wet indoors environments release mycotoxins harmful to humans. Effects are usually allergic reactions, infections, and mucous membrane irritation. However, in some cases, especially with exposure to multiple toxigenic molds, effects such as bleeding lungs, vomiting, and intestinal hemorrhage are seen. The greatest danger is to children under the age of one.

Source: Water damaged porous woods, high humidity areas with inadequate ventilation.

What To Do: Dry things out, and clean thoroughly. Dehumidifiers are a big help. For cleaning, use a bleach-water solution mixture of 1 Part Chlorine Bleach to 10 Parts Water. http://www.toxic-black-mold-info.com/moldhealth.htm

4. Formaldehyde- colorless, pungent-smelling gas causes watery eyes, burning sensations in the eyes and throat, nausea, and difficulty in breathing. Can trigger asthma attacks, wheezing and coughing; fatigue; skin rash; severe allergic reactions. May cause cancer.

Source: Pressed wood products like hardwood plywood wall paneling, particleboard, fiberboard. Also furniture made with pressed wood products, urea-formaldehyde foam insulation, durable press drapes, carpets, and glues.

What to Do: Avoid pressed wood products and other formaldehyde-emitting goods in your home. Throw out all that cheap IKEA furniture and shelving! Good ventilation also helps. http://www.epa.gov/iaq/formalde.html

5. Carbon Monoxide- Odorless, colorless gas which causes 500 accidental deaths each year. Can also cause flu-like headaches, vomiting, and nausea.

Source: blocked furnace ducts, car exhaust fumes, blocked fireplace chimneys, and improper use of propane heaters indoors.

What to Do: Annual inspections on fuel-burning appliances to ensure proper ventilation. Install carbon monoxide detectors in your home, one near the furnace and one outside each bedroom. Keep the batteries fresh. http://www.epa.gov/iaq/co.html

6. Lead- Causes adverse health effects on the central nervous system, kidney, and blood cells at low exposure levels. High levels can cause convulsions, coma, and even death. Impairs mental and physical development in fetuses and children. Tissues of small children are more sensitive to the damaging effects of lead.

Source: Lead-based paint, banned for residential use since 1978, still common in homes built prior to 1960, usually under layers of newer paint. Painted windows and doors flake toxic airborne dust when opened and shut.

What to Do: Leave lead-based paint undisturbed if it is in good condition; do not sand or burn off paint that may contain lead. Lead paint in good condition is usually not a problem except in places where painted surfaces rub against each other and create dust (for example, opening a window). Leave lead-based paint removal to a specialist. During renovations to remove lead-based paint, residents, especially children and pregnant women, should leave the building until all work is finished and clean-up is done. http://www.epa.gov/iaq/lead.html

7. Polyurethane Foam or Fiberglass Insulation- In a house fire, these will burn and release carbon monoxide, nitrogen oxides, and traces of hydrogen cyanide, which is lethal. (Note: fiberglass insulation itself is fairly harmless in a fire- it’s the resins and facing material that give off the toxic vapors.)

Source: Smoke inhalation in a burning house.

What to do: Avoid foam insulation. Keep a set of gas-masks in the house if you can’t. http://www.cdc.gov/NASD/docs/