Working at night could lead to higher risks of developing cancer, according to the World Health Organization.

Exposure to light while working the night shift might create hazardous exposure equal to that from ultraviolet radiation, diesel engine exhaust or anabolic steroids, according to a published report on the WHO study. The findings are an interpretation of an analysis by the WHO’s International Agency for Research on Cancer in the December issue of the journal Lancet Oncology. The IARC reportedly plans to classify night shift work as a “probable” carcinogen.

Previous studies have shown that some cancer rates are higher in certain instances for women, men and test animals subject to long periods of night work or alternating shift routines. Researches have theorized that disturbed circadian rhythms might lower the production of a key hormone, and that lack of sleep breaks down the immune system.