Less obvious is the presence of suspect chemicals used to manufacture carpets that "off gas" and can fill the room. The most common is formaldehyde, which will not only irritate the nose and throat, trigger asthma attacks and cause other lung damage, but could, based on laboratory studies on animals, cause cancer, according to the EPA.
Carpets are concerning enough that the American Lung Association recommends avoiding them completely. (If you already have one, the association recommends using a HEPA [high efficiency particle air] vacuum.) There are carpets on the market that are made with nontoxic materials (though they can still harbor dirt, dust and dander like any other rug).
Spray bottles, sponges and the cleansers that break up dirt are supposed to leave your home cleaner, but many can also introduce unhealthy compounds into the air.
The first thing that must be said is: Never mix a chlorine-based cleanser with an acid-based cleanser, like vinegar or ammonia. Don't even clean the same surface with one and then the other. The result of mixing these two cleansers is potent -- often deadly -- chlorine gas. That's the same chlorine gas that ties counter-terrorism experts up in knots. You don't want it in your house.
The larger point, though, is that many off-the-shelf cleansers contain powerful and often toxic solvents, antibiotic pesticides and other nasty chemicals. Chlorine is poisonous. Many household cleansers are unnecessarily hazardous, given that simple recipes with vinegar, baking soda and the like will do just as good a job without any of the risks.
Cabinets, furniture, shelving, countertops and any other household item made with pressed wood is likely stuck together with glue that contains formaldehyde.
As with rugs, the formaldehyde in the glue will "off-gas" over time, releasing small amounts into the air in your home.
To avoid formaldehyde, avoid pressed wood products unless you know they are free from formaldehyde.
The Kitchen Stove
Just the simple act of cooking on the stove, particularly a gas stove, can actually introduce unsafe levels of nitrogen dioxide into the air, increasing the risk of asthma attacks and other respiratory illness. Also a concern is simple steam, which can do the same work as moisture in the bathroom at promoting unwanted mold growth.
The better solution is simply to properly ventilate your stove so that the exhaust vents to the outdoors.