Forget that old squabble about which is smarter, dogs or cats. They're both smart. Look at them, lying there in the only patches of sunshine in the house, lazily hogging the beams as the sun shifts. It's almost as if they were addicted. "Well, of course we are," they would say if they could talk. Lying in the sun just feels so good. And you humans needed a scientific study to tell you that? Apparently we did. A report published in the July issue of the Journal of the American Academy of Dermatology (and causing a lot of nervous scoffing by tanning-salon proprietors) confirms what dogs and cats already knew.

Soaking up the sun isn't mainly about acquiring a bronze glow for the beach, although that's a bonus for hairless, pale-skinned humans. It's about getting an all-around mood boost -- and it's arguably addictive. Which means that tanning-bed devotees might find it much harder than they thought to resist those warnings by dermatologists about the dangers of overexposure to ultraviolet light.

Researchers in North Carolina set up a cunning experiment. Fourteen people were invited to tan twice a week, splitting the time between a bed that emitted UV light and one that didn't, though they looked identical. The subjects' moods were measured before and after each session and were found to be noticeably better after they had used the UV beds. The subjects were then invited back for an optional weekly third session and told they could choose between the beds. Twelve of the 14 chose to come back and, of those, 11 picked the UV bed every time.

It was "reinforcing," said the study's lead author, Dr. Steven Feldman of Wake Forest University School of Medicine. "They would say, 'This is the bed that relaxes me more.' " They were "getting their little hit of UV," he added. Asked why UV light seems to make people (and pets) feel better, Dr. Feldman speculated that such light releases endorphins, the "feel-good" neurochemicals also triggered by exercise and certain drugs, a theory he said he planned to test.

Whatever the mechanism, the findings are of considerable interest to a society such as Japan's, in which tanning salons are big business. Tanning used to mean treating hide to turn it into leather. It still does, in a way, only now it also applies to human hide -- and as such has become a lightning rod for debate, although with no evidence that the antagonists are even listening to one another. On one side are public-health experts, who long ago established the link between sun exposure and skin cancer. On the other are the young, especially teenage girls, for whom beauty doesn't mean the traditional Japanese ideal of alabaster skin but a tan so dark it's almost orange, accompanied by sun- or chemical-lightened hair.

That tan can be acquired three ways: by sunbathing; by applying lotion; or by visiting a tanning salon. The first method is free, but slow and sweaty; the second is cheap but unreliable (who wants patches?) and does nothing for your mood; the third costs the most but is quick, easy, efficient and evidently provides a relaxing buzz without the drugged feeling you get from sitting in the hot sun all day. Unfortunately for the conformist young, the only method that doesn't damage their skin is also the least appealing, and the one that damages it the most (since tanning booths provide more intense doses of UV light than the sun) is the most appealing.

That is why the U.S. study is so disturbing, suggesting as it does that the harmful tanning craze may be harder to overcome than doctors and public-health officials had hoped. If ultraviolet light can actually trigger a physiological addiction -- like nicotine, say -- then people might have trouble giving up their regular "hits" even if the invisible fashion gurus were to rule tomorrow that pale skin was back in vogue.

What to do? In the United States, lawmakers have sought to restrict access to tanning salons by anyone under 18, and Dr. Feldman suggested last week that tanners who think they might be addicted could request medications known to help people kick other addictions, such as smoking. Both responses seem sensible.

The hazards of tanning also seem like a fit subject for an official public-relations campaign. Back in July 1998, the Health Ministry took a baby step forward when it replaced the word nikkoyoku (sunbathing) in its child-rearing advice booklet with gaikiyoku (going outside and getting fresh air), so mothers wouldn't think sun was a good thing for infant skins.

Now would be an appropriate time to extend that concern to tan-happy teenagers. How about a slogan for buses and billboards? "UV: Just let the dog have it."