Ultraviolet (UV) rays are known to cause skin cancer at high exposures, and yet very little safety research has been done on the lamps used to dry nail polish in beauty salons.

Now a new study by researchers at the University of California San Diego and the University of Pittsburgh in the US has uncovered concerning evidence of the damage that this overlooked source of radiation could be causing to our hands.

LED nail polish dryers look like little tanning beds for your hands. They use UV light to cure and dry some types of nail polish quickly and cleanly.

The bulb on an LED nail polish dryer is less intense and has a different UV spectrum to a tanning bed, but the few rays it emits still easily penetrate the skin with unknown results.

While previous studies have shown little to no link between nail drying machines and skin cancer at a population level, a new study on the molecular side of things has turned up some concerning results.

Bioengineer and lead author Ludmil Alexandrov says before the study "there was zero molecular understanding of what these devices were doing to human cells."

The experiment's findings suggest UV light from nail lamps can damage the DNA of human and mice cells in similar ways.

When petri dishes of mouse and human cells were put inside a nail polish dryer for two 20-minute sessions (separated by an hour break), about 20 to 30 percent of the cells died.

Meanwhile, 20 minutes of exposure a day for three days back-to-back killed up to 70 percent of exposed cells. For a single manicure, a person sticks their fingers under UV light for about 10 minutes in total. The exposure in the current study was extreme by comparison.

Cells that remained after the total exposure period showed signs of DNA damage and mutations linked to skin cancer.

While these results do not provide direct evidence of increased cancer risk, they do indicate that an appreciable level of risk could be present. Exactly how often someone needs to visit a nail salon to put themselves in danger's way remains to be determined.

Alexandrov and his colleagues are calling for proper long-term epidemiological studies to assess whether the mechanisms uncovered by the test translate into actual harm.

One of the members of Alexandrov's lab and first author of the study, Maria Zhivagui, was so alarmed by the results, she decided to stop getting regular gel polish manicures.

"Once I saw the effect of radiation emitted by the gel polish drying device on cell death and that it actually mutates cells even after just one 20-minute session, I was surprised," Zhivagui says.

Zhivagui is being extra cautious. To her, the possible risks outweigh the benefits. But that doesn't mean everyone needs to stop getting gel polish manicures immediately.

The risk of developing cancer on the hands from UV nail lamps seems to be very low at a population level among those under the age of 65. Some researchers have interpreted these results as meaning "gel manicures have little to no carcinogenic risk."

But the risk to the individual is something cancer scientists are not dismissing quite yet.

Concerned customers, they say, should slather up with sunscreen before their manicures. Either that or they should wear gloves with finger holes.

Dermatologist Melissa Piliang from Cleveland Clinic warned in 2021 that people who visit the nail salon more frequently will probably face a greater risk, if one does exist.

If someone is going a few times a year, they probably don't have much to worry about. If they're going once every two weeks, it may be more cause for concern.

In 2009, two healthy women who got regular manicures and who had no family history of skin cancer, suddenly developed skin cancer on their hands. The two case studies prompted researchers to dig into the health risks of nail polish dryers further.

In 2013, researchers confirmed that the dose of UV radiation emitted by UV nail lamps was 4.2 times stronger than the Sun. The authors concluded that the high intensity of the exposure warranted further studies.

While these products are marketed as safe, the reality is that very little research has been done on their health risks, and case studies are not enough to prove cause and effect.

But researchers hired by product testing companies responded by saying there was no "cause for public alarm". The dose of UV light used in a single nail painting session is trivial in the grand scheme of things, they argued.

The authors of the 2013 paper stood firm. They pointed out in a published rebuttal that, unlike the other researchers, they had no conflicts of interest and only wanted to know the truth.

Published opinions based on observational studies have done little to improve our understanding of the health risks posed by UV lamps.

It's high time for some independent epidemiological research.

"It is likely that such studies will take at least a decade to complete and to subsequently inform the general public," Zhivagui, Alexandrov and colleagues write.

In the meantime, it will be up to customers to weigh the risks and benefits.

The study was published in Nature Communications.