Cigarette smoking is harmful, not only to the smoker, but to those around the smoker who are forced to breathe in the secondary smoke. Most lung cancer is caused by cigarette smoking. Exposure to other people's tobacco smoke increases the risk of lung cancer among nonsmokers. Scientists have found that nonsmokers who live or work with smokers have a higher lung cancer risk than nonsmokers who don't have this type of exposure to tobacco smoke. The immediate effects of breathing secondhand smoke include an increase in heart rate and blood pressure, and dangerous levels of carbon monoxide in the blood. The smoke from the burning end of a cigarette is filled with hundreds of dangerous chemicals and contains more tar and nicotine than the smoke that's directly inhaled by the smoker. While adults can try to avoid being in smoky areas, children and infants are especially vulnerable. Studies show that babies whose parents smoke are hospitalized twice as often for conditions such as bronchitis and pneumonia. Children under the age of two are particularly susceptible because their lungs and immune systems aren't fully developed. The symptoms of children with asthma can also be aggravated by living with smokers. As awareness of the dangers of secondhand smoke continues to rise, communities around the country are banning smoking from public buildings and areas. For more information about secondhand smoke, consult your healthcare provider.