Photographs: Reinhard Krause/Reuters.
Window cleaners make about $25 a day. The maximum they can earn in a day is $1000, according to Wikimedia.
However, the job comes with a number of risks, like slipping on water or soap, and falling from heights. Window cleaning is considered the most dangerous job in the UK.
The cleaners have to obtain a license for high-rise operations and must not have high blood pressure or naturally suffer a fear of heights.
They are not allowed items which could fall, such as cell phones or wristwatches, and must stop working when it is too windy.
Take a look at the tough lives of these window cleaners...
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The tough life of window cleaners
Photographs: Aly Song/Reuters.
Migrant labourers wash a roof near The Bund on the banks of the Huangpu River in Shanghai.
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The tough life of window cleaners
Photographs: Luke MacGregor/Reuters.
People watch as a window cleaner works outside the 14th floor at the Shard in London.
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The tough life of window cleaners
Photographs: Toru Hanai/Reuters.
Window washers work on a building near a ferris wheel in Tokyo's Odaiba entertainment and shopping district.
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The tough life of window cleaners
Photographs: Marcos Brindicci/Reuters.
Workers clean windows at a building in downtown Buenos Aires.
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The tough life of window cleaners
Photographs: Issei Kato/Reuters.
A worker cleans the windows of an office building in Tokyo.
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The tough life of window cleaners
Photographs: David Gray/Reuters.
Cleaners watch an Air China plane land as they sit atop the roof of the Beijing Capital International Airport's train station.
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The tough life of window cleaners
Photographs: Jason Lee/Reuters.
A worker cleans the windows of an apartment block on a haze day in central Beijing.
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The tough life of window cleaners
Photographs: Reuters.
Cleaners prepare for window cleaning outside the 101st floor of the Shanghai World Financial Center.
More than 30 workers on the window-cleaning team of the skyscraper work in pairs every day.
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The tough life of window cleaners
Photographs: Jason Lee/Reuters.
A worker cleans the windows of an apartment block in central Beijing.
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The tough life of window cleaners
Photographs: Reuters.
Workers clean the exterior of the 'Sun Valley' at the World Expo site in Shanghai.
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The tough life of window cleaners
Photographs: David Gray/Reuters.
A cleaner abseils down the side of a newly renovated building in central Beijing.
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The tough life of window cleaners
Photographs: Toru Hanai/Reuters.
A window cleaner dressed as Santa Claus poses for photographers during an event to celebrate the upcoming Christmas holiday season at a shopping mall in Tokyo.
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The tough life of window cleaners
Photographs: Tobias Schwarz/Reuters.
Window cleaners work at an office building at Berlin's Kurfuerstendamm shopping mall.
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The tough life of window cleaners
Photographs: Yuriko Nakao/Reuters.
A worker cleans a window of an office building in Tokyo.
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The tough life of window cleaners
Photographs: Reuters.
Workers clean the windows of a newly built office building in Taiyuan, Shanxi province.
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The tough life of window cleaners
Photographs: Stoyan Nenov/Reuters.
A worker cleans the windows of a hotel building in downtown Sofia.
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The tough life of window cleaners
Photographs: Ricardo Moraes/Reuters.
A cleaner washes the glass windows of a building in Brasilia.
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The tough life of window cleaners
Photographs: Daniel Aguilar/Reuters.
A worker cleans the windows of a hotel in central Mexico City.
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The tough life of window cleaners
Photographs: Guillermo Granja/Reuters.
Workers clean the windows of a building in Quito.
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The tough life of window cleaners
Photographs: Reuters.
Window cleaners stand on a platform hanging from the front of the CCTV (China Central Television) building on a sunny day in central Beijing.
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The tough life of window cleaners
Photographs: Vincent Kessler/Reuters.
Employees clean the windows of the main building of the European Parliament in Strasbourg.
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The tough life of window cleaners
Photographs: Jumana El Heloueh/Reuters.
Sailors clean windows for the watchstanders inside the Flag Bridge of the Nimitz-class aircraft carrier USS Abraham Lincoln (CVN 72) looking for surface and air contacts during a transit through the Strait of Hormuz.
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The tough life of window cleaners
Photographs: Dylan Martinez/Reuters.
A cleaner washes the window of the athletes' hotel in Istanbul. Athletes from around the globe are in Turkey ahead of the World Indoor Athletics Championships on Friday.
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The tough life of window cleaners
Photographs: Reuters.
A worker cleans the window of an office building in Taiyuan, Shanxi province.
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