Sidestream smoke is more dangerous for people to inhale. A non-smoker inhales this whenever they're around someone who is smoking. Sidestream smoke actually has higher concentrations of some harmful compounds than the mainstream smoke the smoker inhales. The smoke at the end of a burning cigarette has more particles that are smaller and more harmful than the mainstream smoke. They go deeper into the lung tissue and do more damage.
Carbon monoxide causes a greater lack of oxygen in non-smokers.
With reduced oxygen, the heart, lungs, and brain cannot function properly. This leads to permanent brain and vascular change. Studies show that there are several cancer-causing substances as well as more tar and nicotine in sidestream smoke than mainstream smoke, and it can cause death from heart disease. Many studies show that in a person's first wo years of life, babies of parents who smoke at home have a much higher rate of lung diseases such as bronchitis and pneumonia than babies with non-smoking parents. Infants and children have tender tissues and are more susceptible to passive smoke.