Researchers say that there is no safe level of exposure to secondhand smoke. In this “8 Ways to Prevent Cancer” segment, Siteman Cancer Center research member Douglas Luke, PhD, says studies have shown that exposure to secondhand smoke over time increases lung cancer risk by 20 percent to 30 percent. Researchers at Siteman have also found that buildings with smoke ventilation systems still have high nicotine levels in the air when smoking is taking place. At times, they even have higher nicotine levels in the air than buildings without ventilation systems.
Source: The Dangers of Secondhand Smoke