Environmental tobacco smoke (ETS) is at the top of the list of carcinogenic environmental toxins.  Poor indoor air quality if often the result of poor ventilation resulting from more efficient construction practices in sealing homes and office buildings from the outdoor environment. Reduced ventilation has resulted in the "Sick Building Syndrome" (SBS) with symptoms such as headache, fatigue, malaise, mental confusion, eye and throat irritation, and coughing and wheezing. Assessing the relationship between exposure to air pollutants and disease is complicated by the problem of multiple exposure to a multiple pollutants. Multiple chemical sensitivity (MCS) may develop through the combined effects of a number of chemicals in concentrations that are not be harmful alone.

Indoor air pollution can be the result of occupational exposures, hobby or recreational chemicals, carpets and furniture or indolent materials present in the air because of poor building ventilation or contamination. While all of these are potentially harmful, the occupational exposures may be the most risky. At work, volatile organics such as gasoline, cleaning solutions and solvents, and other organic chemicals can be health hazards.

The nose removes some inhaled pollutants that  cause local tissue swelling and chronic obstruction of the sinuses. Some chemicals are absorbed through the nasal mucosa and into the systemic circulation, causing the body to attempt detoxification of the chemicals by oxidation, reduction, conjugation, and/or degradation. During the detoxification process, pollutants may become even more toxic than they were in their unoxidized forms. These pollutants may produce subtle, but important changes in the body, such as reduced T-suppressor cell activity. This suppression leads to a relative increase in the activity of B-helper cells, which then produce an excess of immunoglobulins, and therefore an increase in allergic phenomena.