The U.S. Environmental Protection Agency has found that concentrations of pollutants can be up to 100 times higher indoors than outdoors, so air pollution isn't just an outside problem.
Items inside the home that release gas are the primary cause of indoor air problems. The list includes carpeting, upholstered furniture, gas appliances, paints and solvents, cleaning products, air fresheners, dry-cleaned clothing and pesticides. If you have an attached garage, fumes from the gasoline, oil and antifreeze in your car can find their way into your home's air. Harsh chemicals can also come from cigarette smoke and woodstoves.
As far as allergens in your home, it's not just your dog or cat that's the culprit. Pollen particles can blow into your home through open windows, and people and pets can track them inside. Damp areas in your home can quickly lead to mold and mildew buildup. Textile fibers from clothing, curtains and other fabrics produce and collect dust.