Second-hand smoke is indeed much more harmful than first-hand smoke, because when the smoker inhales the cigarette, only 10% of the smoke produced by the cigarette is inhaled into the lungs of the smoker, and the rest of all the smoke will be emitted into the air. At this time, in the smoke formed by secondhand smoke, the non-smoking people around inhale relatively more harmful substances, and are naturally more harmed. In addition, the duration of secondhand smoke is longer than that of firsthand smoke. Because the smoke of first-hand smoke may last 5-10 minutes, but the smoke of second-hand smoke spread in the air may last for half an hour, or even an hour or more to dissipate. People around passive smokers, in the environment of secondhand smoke, suffer the harm for a longer period of time.