Glenda Fuster lies in a tanning booth at the Run to the Sun tanning salon in Anchorage, Alaska. (Al Grillo/Associated Press)

Tanning beds and ultraviolet radiation cause cancer and have been moved up to the highest risk category by international cancer experts.

The new classification means tanning beds and UV definitely cause cancer in humans, just as tobacco smoke, the hepatitis B virus and mustard gas do.

The International Agency for Cancer Research or IARC, the World Health Organization's cancer wing in Lyon, France, updated the level based on research published online Wednesday in the medical journal Lancet Oncology.

"People need to be reminded of the risks of sunbeds," said Vincent Cogliano, one of the study's authors. "We hope the prevailing culture will change so teens don't think they need to use sunbeds to get a tan."

Until now, tanning beds and UV were considered "probably carcinogenic to humans."

Experts upgraded the level after a comprehensive analysis of about 20 studies concluded that the risk of skin melanoma is increased by 75 per cent when people started using tanning beds before age 30.

Risk level raised for all UV, ionizing radiation

Until now, only UVB radiation from solar rays was known to cause a genetic mutation.

But researchers found the same mutation in the skin of mice treated with UVA. The agency decided to reclassify all types of ultraviolet radiation — UVA, UVB and UVC — as carcinogenic to humans or Group 1 carcinogens.

Previously, the three UV types were grouped as probable carcinogens.

Kathy Banks, chief executive of The Sunbed Association, a European trade association of tanning bed makers and operators, disputed the classification of tanning beds as carcinogenic.

"The fact that is continuously ignored is that there is no proven link between the responsible use of sunbeds and skin cancer," Banks said in a statement.

Most people who use tanning beds use them less than 20 times a year, she said.

Dangerous for minors

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.

With files from The Associated Press