One in five sunbed users may be "addicted" to the devices, leading skin doctors have warned.
A new study has found that 19.7% of users show symptoms of indoor tanning addiction.
The finding comes as researchers tested a new way to screen users for addiction.
Their study, published in the British Journal of Dermatology, examined the Behavioural Addiction Indoor Tanning Screener - which entails a brief survey of users to examine addictive behaviours, such as experience of diminished control or urges or craving for the experience.
A team of German and US researchers found that among 330 current users of sunbeds in Germany, 19.7% screened positive for symptoms of a potential indoor tanning addiction.
This compared with 1.8% of 553 former users who had not used a tanning bed in the last year.
Commenting on the study, Nina Goad, of the British Association of Dermatologists, said: "This is an interesting pilot study with two important developments: the first is a new way of measuring symptoms of tanning addiction in a large population group.
"The second is the finding, on testing this method, that as many as one in five sunbed users may have symptoms of addiction.
"There is strong evidence that use of sunbeds increases the risk of skin cancers, including malignant melanoma, which is the most deadly type.
"For people who start using sunbeds before the age of 35 years, the relative risk of malignant melanoma almost doubles.
"If indoor tanning does indeed have addiction potential, being able to assess the scale of the problem will be imperative.
"It certainly would help to explain why so many people continue to use sunbeds despite knowing the risks."