Nitrogen Dioxide - is a reddish-brown, irritating odor gas that can be a byproduct of indoor fuel-burning appliances, such as gas stoves, gas or oil furnaces, fireplaces, wood stoves and unvented kerosene or gas space heaters.

Dust Mites - are too small to be seen, but can be found in almost every home in mattresses and bedding materials, carpets, upholstered furniture, stuffed toys and curtains.

Mold - can grow indoors when mold spores land on wet or damp surfaces. In the home, mold is most commonly found in the bathroom, kitchen and basement.

Secondhand Smoke - is a mixture of smoke from the burning end of a cigarette, pipe or cigar and the smoke exhaled by the smoker that is often found in homes and cars where smoking is allowed.