Sunbathing may be a physical addiction, research in the United States suggests.
Sun beds are popular with the young
Scientists believe exposure to ultraviolet rays may stimulate the release of chemicals in the blood which produce a natural high.
The team from Wake Forest University in North Carolina say this may explain why some people are prepared to ignore the cancer risk of too much sun.
The research is published in the Journal of the American Academy of Dermatology.
The Wake Forest team analysed 14 people, aged between 16 and 34, who typically used tanning beds two times a week.
Each volunteer spent 15 minutes lying on a sunbed which exposed them to UV rays and then on another - again for 15 minutes - which released no rays.
The volunteers were not told which beds released UV.
The subjects were asked if they would like to return days later and use a sunbed of their own choosing.
Twelve returned and 95% opted for the bed which radiated UV light. They said it made them feel good and helped them relax.
The researchers believe that tanning may release endorphins into the bloodstream.
The same chemicals are responsible for the 'feel-good factor' after exercise.
Frequent tanners may become addicted to the feelings induced by the chemicals, it is believed.
Lead researcher Professor Steven Feldman said: "We believe that ultraviolet light has an effect on mood that tanners value.
"We believe these relaxing effects contribute to tanning behaviour and may help explain why people choose to tan despite the risks."
The British Association of Dermatologists warns that the long-term effects may include premature ageing, skin cancer and an increased risk of cataracts.
The British Medical Association has also advised people not to use sunbeds.
UV light occurs naturally in sunlight and is responsible for the tanning and burning effects of the sun. Artificial UV light is used in tanning beds and sunlamps.