The good and the bad

Are you one of those people who likes to lie in the sun, slowly turning to get an even tan, like a chicken in a rotisserie? A study is causing a stir by suggesting that you may be addicted to the sun—and that this is why you accept the risk of skin cancer.

The team of Gillian Fell and David Fisher, from Massachusetts General Hospital in the US, exposed hairless mice to ultraviolet (UV) radiation for six weeks, five days a week, for the equivalent of half an hour of midday sun for a human. The radiation causes skin cells to produce pro-opiomelanocortin, a peptide that gives rise to the hormone that stimulates the production of melanin, the pigment that gives skin its much-desired tan.

But the same peptide also turns into endorphin, produced in the skin and distributed to the body and brain. Endorphin, like a good opioid, is analgesic, reducing the sensation of pain in the skin (such as that caused by burns). And it also gives... pleasure.

Irradiated animals showed signs of opioid withdrawal syndrome after administration of naloxone, which blocks the action of endorphins. In addition, these animals avoided staying in the box where they were treated with naloxone, preferring the other box, where they could enjoy the effects of elevated endorphins in peace.

But to say that the animals became addicted to UV rays, and that therefore exposure to the sun is addictive, is another matter entirely. For starters, being good (for example, producing endorphins) is not enough to cause addiction. Drinking water is delicious and pleasurable when you are thirsty—but we always drink the same amount of water when we feel thirsty. Addiction, on the other hand, is something that must be obtained in increasing amounts because the pleasure obtained decreases as the brain adapts. The study shows that UV rays are pleasurable—but it does not show that they are addictive.

It makes evolutionary sense that UV exposure is pleasurable. Although radiation is harmful and damages the skin, it is necessary for the body to produce vitamin D. Endorphins reward this and other behaviors, such as sex, and increase the chances of them happening again.

Excessive exposure, however, is up to each adult, who is perfectly capable of understanding the well-known and widely publicized risks. I can already foresee the day when “addicts” will want to absolve themselves of blame for their “illness” and demand compensation... well, it won't be from the sun.

Excerpt from Suzana Herculano-Houzel (2025) Neuroscience of Everyday Life, originally published in Folha de São Paulo in June 2014