Doctors have seen an increase in the number of young people with skin cancer as use of tanning beds has increased among those under 30.
Previous studies found younger people who regularly use tanning beds are eight times more likely to get melanoma than people who have never used them.
WHO has warned people younger than 18 to avoid tanning beds. The Canadian Cancer Society has called for minors to be barred from using tanning beds, and the American Cancer Society advises people to try bronzing creams instead of tanning beds.
The expert working group also classified all types of ionizing radiation, such as radon gas, plutonium and radium and their decay products and radio-iodines, as Group 1 carcinogens.
The group also concluded there is enough evidence for ocular melanoma in welders, but because they are exposed to other harmful agents, the risk could not be attributed specifically to UV radiation.