Mold and pests
Plumbing leaks and poor insulation are the main cause of mold and pests, says Steorts.
Some materials, such as synthetic stucco, are easy to puncture and may allow moisture to seep in, says Vimal Kapoor, president of the Building Inspector of America, based in Germantown.
An alarm should go off, he says, "if you feel better when you're out of the house."
Mold tends to worsen respiratory illnesses, induce asthma attacks and irritate eyes and nasal passages, according to the Centers for Disease Control and Prevention. Some studies also suggest more severe effects, including flu-like symptoms.
More surprisingly, cockroaches can be potential triggers of asthma symptoms among children allergic to them, says Stephen Teach, an emergency room physician at Children's National Medical Center who also runs the asthma clinic.
Decomposing cockroach bodies and their excrement easily become airborne, and can be inhaled into the bronchial tubes.
Other household allergens include dust mites and grease.
Every six months, look for signs of pests and mold and mildew. If you are suspicious about toxins or mold, have an air quality test, experts say.
When the carbon monoxide detector went off in her Arlington, Va., rental, Morley and her roommates unplugged it. Like many, they assumed the problem was with the detector.
They were wrong.
Because carbon monoxide is colorless and odorless, too often, homeowners don't realize there's a problem.
After comparing symptoms of headaches and nausea, Morley and her roommates plugged back in the detector, which sounded a piercing alarm. The fire department confirmed high carbon monoxide levels. Faulty appliances were to blame.
"It was scary," says Morley, who was treated with oxygen at the hospital.
Exposure can cause a range of flu-like symptoms, including headaches, dizziness and nausea. But carbon monoxide exposure also can be fatal. Each year, more than 400 deaths are blamed on CO poisoning, according to the CDC.
Gas fireplaces, furnaces, generators and appliances cause most carbon monoxide leaks, says Steorts. She recommends that her clients check whether appliances have been recalled, and that appliances and heating and cooling systems be inspected annually.
In addition to installing CO detectors, examine all seals around doors and windows annually, paying close attention to the door between house and garage, because CO can leak into homes from cars, Steorts says.