Secondhand smoke is produced by a burning cigarette or other tobacco product. An estimated 4 million children a year get sick from being around secondhand smoke. Parental smoking has been shown to affect the lungs of infants as early as the first 2 - 10 weeks of life, and such abnormal lung function could persist throughout life.

Exposure to secondhand smoke in the home increases the risk for asthma and asthma-related emergency room visits in children who have existing asthma.

Parental smoking is believed to increase the risk for lower respiratory tract infections (such as bronchitis or pneumonia) by 50%. Environmental exposure to smoke is thought to be responsible for 150,000 - 300,000 such cases every year.