, the average life expectancy at birth in China is 76 years, and the infant mortality rate is 7 per thousand. Both have improved significantly since the 1950s. Rates of stunting, a condition caused by malnutrition, have declined from 33.1% in 1990 to 9.9% in 2010. Despite significant improvements in health and the construction of advanced medical facilities, China has several emerging public health problems, such as respiratory illnesses caused by widespread air pollution, hundreds of millions of cigarette smokers, and an increase in obesity among urban youths. China's large population and densely populated cities have led to serious disease outbreaks in recent years, such as the 2003 outbreak of SARS, although this has since been largely contained. In 2010, air pollution caused 1.2 million premature deaths in China.