Participants pass an egg using their mouths during a religious ritual as they play the role of traditional fighters in a parade during the Popo (Mask) Carnival of Bonoua, in the east of Abidjan, April 18, 2015. The carnival has its origins in the changes that Aboure youths in Bonoua introduced to the annual festival of yams. (Photo by Luc Gnago/Reuters)

Ethnic Miao men wearing traditional masks smear dust on a woman's face to wish her good luck during local celebration event for Lunar New Year in Liuzhou, Guangxi Zhuang Autonomous Region, China, February 16, 2016. (Photo by Reuters/Stringer)

Penitent Jerry Mazon, 9, wears his “Morions” mask while playing with his baby brother during Holy Week celebrations in Mogpog, Marinduque in central Philippines March 22, 2016. (Photo by Erik De Castro/Reuters)

An anti-government protester wearing a Guy Fawkes mask stands with a shield near flames from molotov cocktails thrown at a water cannon by anti-government protesters during riots in Caracas in this April 20, 2014 file photo. (Photo by Jorge Silva/Reuters)

Demonstrators wear skull masks during an anti government protest, as Chile's President Michelle Bachelet delivers a speech inside the National Congress, in Valparaiso city, Chile May 21, 2016. (Photo by Ivan Alvarado/Reuters)

The manager of Jinhua Partytime Latex Art and Crafts Factory wears a mask of U S. Democratic presidential candidate Bernie Sanders as he poses and gives a thumbs-up as during a presentation of products to reporters at his factory's showroom in Jinhua, Zhejiang Province, China, May 25, 2016. (Photo by Aly Song/Reuters)

A masked Kashmiri protester shouts freedom slogan near burning tires set up as road blockade by protesters in Srinagar, Indian controlled Kashmir, Tuesday, July 19, 2016. The largest street protests in recent years in the disputed region, that left dozens of people dead and hundreds injured erupted more than a week ago after Indian troops killed a popular young rebel leader. (Photo by Dar Yasin/AP Photo)

People in Kathmandu joke that the face mask has now become part of the national dress – an indispensable accessory in an effort to protect themselves from the dust. Nepal has the worst air quality in the world, according to the Environmental Performance Index. (Photo by Pete Pattisson/The Guardian)