Tanning salons in Blackpool have been told to improve after large numbers of sun beds failed safety checks.
Blackpool Council tested 110 sun beds at 45 salons in the resort and found 80 had bulbs which emitted higher than recommended levels of UV light.
Eleven shops were tested for under-age sales with seven found to be allowing under-18s to use sun beds illegally.
Businesses have now been warned to comply with safety standards or face prosecution.
Councillor Gillian Campbell, Blackpool Council's cabinet member for public protection, said the findings were "shocking".
She said: "I would urge consumers who use sun beds to take great care.
"People need to make wise choices and ensure they are not putting themselves at risk of skin cancer."
Dr Arif Rajpura, Blackpool Council's director of public health, said: "We know that using sun beds can cause malignant melanoma, the most serious form of skin cancer.
"Consider a safe tanning alternative instead and now that we are coming into spring and hopefully better weather, remember to enjoy the sun safely whether at home or abroad, use shade, clothing and at least SPF30 sunscreen to protect yourself and your kids."
Gary Lipman, chairman of The Sunbed Association, said he was "delighted" checks were taking place.
"We would always urge sun bed users to seek out a tanning salon in membership of The Sunbed Association, where they can be assured of excellent customer care and advice from properly trained staff," he said.