Other substances contained in ETS are known toxicants and are potentially harmful. The majority of research on secondhand smoke has examined nonsmokers who are regularly exposed to ETS at home or at work. Since some of the more toxic and carcinogenic compounds in tobacco smoke are present in higher concentrations in secondhand smoke, routine exposure to ETS may yield the equivalent of several cigarettes per day. The particles in secondhand smoke are also smaller than those inhaled by smokers, and therefore generally penetrate deeper into the lungs where they are more likely to cause damage. Infants and children with a parent or caretaker who smokes are particularly vulnerable to the hazards of secondhand smoke.
Younger children are more likely to suffer more serious effects.
Children exposed to ETS through parental smoking face an increased risk for middle ear disease and for respiratory infections, such as bronchitis and pneumonia. These children take longer to recover from such illnesses. Exposure to secondhand smoke has also been associated with an increase in the incidence and severity of asthma in children. Like children, adults who are regularly exposed to ETS are also more susceptible to respiratory ailments than those who are not exposed. For individuals who suffer from preexisting asthma and emphysema, secondhand smoke may aggravate symptoms.