The International Agency for Research on Cancer (IARC) has declared that the use of a sunbed or sunlamp is definitively "carcinogenic to humans."
Earlier the agencys assement used to be sunbeds were "probably carcinogenic.
The risk has now been upgraded, it was revealed in the journal Lancet Oncology.
The recommendation follows a review of research which found that the risk of melanoma - the most deadly form of skin cancer - was increased by 75% in people who started using sunbeds regularly before the age of 30.
In addition, several studies have linked sunbed use to a raised risk of melanoma of the eye.
The revised assessment thus puts sunbed use on a par with smoking or exposure to asbestos. The IARC is an expert committee that makes recommendations to the World Health Organization.
However, the Sunbed Association in the UK said there was no proven link between the responsible use of sunbeds and skin cancer.
The charity Cancer Research UK warned earlier this year that heavy use of sunbeds was largely responsible for the number of Britons being diagnosed with melanoma topping 10,000 a year for the first time.
In the last 30 years, rates of the cancer have more than quadrupled, from 3.4 cases per 100,000 people in 1977 to 14.7 per 100,000 in 2006.
Proposals to ban people under the age of 18 from using sunbeds are under consideration by the government in England.