Sun tanning can be highly addictive and often has more to do with how it makes people feel than with how they look, says a US dermatologist who is visiting Australia.
Ultraviolet (UV) light causes cells to release endorphins, the feel-good hormone, says Prof Feldman, a speaker at the annual scientific meeting of the Australasian College of Dermatologists.
"It's like a little hit of morphine."
This explains why some people continue tanning even though it is turning their skin leathery.
"We see patients in their 20s who look like they are in their 40s. They are clearly not tanning to look good, because they look terrible."
Prof Feldman has conducted a study that shows addicts go through withdrawal when given drugs that block endorphins.
In another study frequent tanners chose a tanning bed that gave them UV light over one that had been modified to block the UV.
Both beds looked and felt identical, but the tanners said the UV one was more relaxing.
"That was fairly definitive proof that the UV has an effect that people can feel and it drives their behaviour."
Prof Feldman says his findings are backed by other researchers who have found that UV light stimulates pleasure sensors in the brain associated with other addictions.
A separate beach-based study showed 30 per cent of tanners were addicts.This was based on answers to alcohol-abuse-type questions about how tanning affected them and why they did it even though they knew it was bad for them.
"Some people go to a tanning salon a couple of times a year because they want to look good for a special event. That's not addiction," says Prof Feldman.
"Others go two or three times a week. It's damaging their skin. That's addiction."