Via CNN: Study: Sunbeds as harmful as cigarettes
The International Agency for Research on Cancer (IARC) had previously classified sunbeds as being a "probable" cause of cancer.
However, the agency is now recommending that tanning machines should be moved to "the highest cancer risk category" and be labeled as "carcinogenic to humans".
It followed a review of research that concluded that the risk of melanoma -- the most deadly form of skin cancer -- was increased by 75 percent in people who started using sunbeds regularly before the age of 30.
The IARC also says there is evidence of a link between melanoma of the eye and the use of sunbeds.
In an article in medical journal The Lancet, WHO oncology expert Dr Fatiha El Ghissassi said: "The use of UV-emitting tanning devices is widespread in many developed countries, especially among young women.
"Analysis concluded that the risk of skin melanoma is increased by 75 percent when use of tanning devices starts before 30 years of age.
"Studies provide consistent evidence of a positive association between the use of UV-emitting tanning devices and ocular melanoma -- skin cancer of the eyelid.