Skin cancer specialists in the US say indoor tanning beds are just as dangerous as natural light.
Their research has found the beds can cause more types of tumours than previously thought.
Studies show the bulbs give out a significant amount of dangerous ultra violet light.
The beds are believed to cause melanomas, but are now being linked with other types of skin cancer.
Experts say tanning may also decrease the ability of human cells to repair DNA damage associated with UV exposure.
Dr Shelley Sekula Rodriguez, of the Baylor College of Medicine in Texas, presented the latest findings at a conference in the US.
She said: "There is no such thing as a safe tan. A tan is the skin's response to an injury and every time you tan you accumulate damage to the skin, as well as accelerate the aging process and increase your risk for skin cancer.
"As long as indoor tanning for cosmetic effects is permitted there needs to be increased educational efforts informing the public of the risks of this type of tanning."