Beijing Pants Run

This picture taken on February 23, 2014 shows participants wearing dresses running half-naked in the annual 3.5 km Undie Run held in the Olympic Forest Park smog-covered Beijing. Some 200 participants took part in this event, many of them with gas masks, as dangerous smog blighted swathes of northern China in recent days. (Photo by AFP Photo/STR)

A man dressed as a leopard takes part in the annual 3.5 km undie run at Olympic Forst Park on February 23, 2014, in Beijing, China. More than 200 people who worn only underwear took part in a running race, which aimed at advocating healthy lifestyle and low-carbonlife. (Photo by ChinaFotoPress/Getty Images)

This picture taken on February 23, 2014 shows participants jumping and running as they take part in the annual 3.5 km Undie Run held in the Olympic Forest Park smog-covered Beijing. (Photo by AFP Photo/STR)

People take part in the annual 3.5 km undie run at Olympic Forst Park on February 23, 2014, in Beijing, China. (Photo by ChinaFotoPress/ChinaFotoPress via Getty Images)

This picture taken on February 23, 2014 shows a participant showing his muscles as he takes part in the annual 3.5 km Undie Run held in the Olympic Forest Park smog-covered Beijing. (Photo by AFP Photo/STR)

An expectant mother warms up during the annual 3.5 km undie run at Olympic Forst Park on February 23, 2014, in Beijing, China. (Photo by ChinaFotoPress/ChinaFotoPress via Getty Images)

This picture taken on February 23, 2014 shows a participant dressed up as a leopard posing for a photo in the annual 3.5 km Undie Run held in the Olympic Forest Park smog-covered Beijing. (Photo by AFP Photo/STR)

This picture taken on February 23, 2014 shows participants wearing dresses running half-naked in the annual 3.5 km Undie Run held in the Olympic Forest Park smog-covered Beijing. (Photo by AFP Photo/STR)

This picture taken on February 23, 2014 shows a participant (C) running with a baby doll in the annual 3.5 km Undie Run held in the Olympic Forest Park smog-covered Beijing. (Photo by AFP Photo/STR)

A runner jogs while wearing a diving mask in the Third Undie Run in the Olympic Greens in Beijing, China 23 February 2014. Over 200 participants strip down to their underwear in the freezing cold and haze to run to promote environmentally friendly lifestyles. (Photo by Zhao Bing/EPA)

This picture taken on February 23, 2014 shows a participant (R) running in the annual 3.5 km Undie Run held in the Olympic Forest Park smog-covered Beijing. (Photo by AFP Photo/STR)