Sir: Passive smoking is the inhalation of smoke, called second hand smoke (SHS), or environmental tobacco smoke (ETS) by other than the intended active smoker. It occurs when tobacco smoke permeates any environment, causing its inhalation by people within that environment. Passive smoking can cause cancer and coronary heart disease. Passive smoking can increase a non-smoker’s risk of getting lung cancer by a quarter, and may increase the risk of cancer of the larynx and pharynx. Coronary heart disease can cause a heart attack, angina and can increase the risk of heart failure. It can also increase risk of strokes. Children are especially vulnerable to the damaging effects of second hand smoke. Children exposed to passive smoke are at high risk of respiratory infections, asthma, bacterial meningitis and cot death. For children the majority of exposure of passive smoking happens in homes. Smoke can spread throughout the home, even if you open the windows. Almost 85 percent of smoke is invisible and smoke particles might build up on surfaces of clothes. The smoke can stay in the air for up to 2.5 hours, even if a window remains open. Especially in small-enclosed places like cars, smoke may still be present in large amounts even after the person has stopped smoking. There are two types of tobacco smoke; one is mainstream smoke, which is inhaled through the mouth from the end of cigarette, and second is side stream smoke, which comes from the burning tip of cigarette. Second hand smoke is made up of side stream smoke and exhaled mainstream smoke, mixed with the surrounding air. Frequent exposure to other people’s smoke can increase risk of lung cancer even one is a non-smoker. It is necessary to quit smoking as soon as possible not for oneself but for the ones we love. KIRAN FATIMA Islamabad