More than 1 in 4 deaths of children under 5 years of age are attributable to unhealthy environments. Every year, environmental risks -- such as indoor and outdoor air pollution, second-hand smoke, unsafe water, lack of sanitation, and inadequate hygiene -- take the lives of 1.7 million children under 5 years, say two new WHO reports. The Guardian adds: "A polluted environment is a deadly one -- particularly for young children," says Dr Margaret Chan, director-general of the WHO. "Their developing organs and immune systems -- and smaller bodies and airways -- make them especially vulnerable to dirty air and water." The harm from air pollution can begin in the womb and increase the risk of premature birth. After birth, air pollution raises the risk of pneumonia, a major cause of death for under fives, and of lifelong lung conditions such as asthma. It may also increase the risk of heart disease, stroke and cancer in later life.