Newer homes are built tighter, often without proper mechanical ventilation, trapping the unhealthy chemicals used to treat the flooring, kitchen cabinets and other products builders typically outfit in houses.

"The particle board and plywood under the nice cherry kitchen cabinets is just loaded with formaldehyde," Bower explains, adding that it doesn't go away. Furthermore, the finish used on the cabinets by manufacturers contain much higher doses of formaldehyde, so large that it does burn itself out after six to 12 months.

Moreover, newer and tightly built homes trap the man-made materials and furnishings in which we fill our homes, from building materials to upholstered furniture to synthetic mattresses to household cleaning products.

How to Create Healthier Indoor Air

Whether you've thought about it or not, the number of things conspiring to make your home's air unhealthy is daunting. Even the most motivated of homeowners wanting to clean up the air in the house can become overwhelmed or even depressed by the task.

Both Vogel and Bower say that homeowners don't have to spend much to have or maintain a healthy home. Besides having accurate and reliable information (there's a lot of bad information and supposed fixes someone is willing to sell you), "just good preventative types of activities like good housekeeping" is effective, Vogel says.

• Keep a clean home: Regular housecleaning and vacuuming will help keep many allergens at bay. Most vacuums, however, spew allergens living in your carpets into the air because of porous vacuum filters. Experts recommend high-efficient filters for vacuums or outfitting your home with a central vacuum. Washing bedding regularly in hot water is another excellent way to reduce such problematic allergens as dust mite, cockroach and cat dander, Zeldin says. Removing shoes in your home prevents tracking in unwanted squatters, including dirt, lead, dust and animal feces.
• Maintain your home's systems: Have heating systems checked for possible carbon monoxide and other gases, as well as the fireplace, the air conditioning unit and gas appliances, such as ranges and dryers. "In a northern climate, the No. 1 thing … have your systems checked periodically," Vogel suggests. Installing carbon monoxide detectors is an inexpensive way to prevent death.