A lighted cigarette produces three kinds of smoke, two of which may pose a significant health hazard for people nearby. The first category of smoke is that inhaled by the smoker, accounting for about 25 percent of the cigarette's total nicotine. The second two categories include the smoke exhaled by the smoker, and the smoke trailing from the unfiltered, lit end of the cigarette. The latter, also called 'side-stream smoke', accounts for about eighty percent of all second-hand smoke. It can contain up to 5,000 chemicals, all of which may irritate the respiratory system, and seven of which are generally considered to be extremely hazardous, cancer-causing toxins. In fact, ongoing exposure to such environmental tobacco smoke or ETS (E-T-S) is likely to greatly increase the risk of lung cancer in non-smokers. The health problems arising from second-hand smoke are generally aggravated in children, as their protective mucus membranes and developing respiratory tissues may be more susceptible to irritation. Fortunately, there are a number of laws in place that prohibit smoking in public places, work environments, and other enclosed areas. Non-smoking individuals may also wish to take steps to avoid second-hand smoke by forbidding smoking in their homes. In less controlled environments, it's probably advisable to stay as far from the smoker as possible, increase room ventilation, and ask that smokers not do so around children.