The nail dryers emit primarily UVA light — the same kind of ultraviolet light used in tanning beds — and are used to dry nail polish or to harden a gel manicure. Gel manicures are popular because they create long-lasting, shiny nails through a chemical gel that is painted on the nail in layers and cured under UV light after every coating.

Case reports of two women who developed squamous cell skin cancers on their hands have suggested an association between cancer and the UV nail light devices, but most doctors agree the risk is low.

In the new study, researchers from Georgia Regents University in Augusta conducted a random sampling of 17 different UV nail lamps found in salons to determine how much ultraviolet radiation is being emitted when clients dry their nails under the lights.

The study, published as a research letter this week in the journal JAMA Dermatology, found wide variation in the dose of UVA light emitted during eight minutes of nail drying or hardening. The dose, measured in joules per centimeter squared, ranged from less than one to eight.

DNA damage that can lead to skin cancer is known to occur around 60 joules per centimeter squared, and none of the nail lamps came close to that number. However, the researchers estimated that for most of the lamps tested, eight to 14 visits over 24 to 42 months would reach the threshold for DNA damage to the skin.

Lamps with higher-wattage bulbs emitted the highest levels of UV radiation, but it would not be easy for a salon client to check the wattage before using a machine.

Clients who are concerned about the risk but want to continue getting gel manicures, which require UV light, have a few options. They can skip the lotion-and-massage portion of the manicure and instead coat their hands with sunscreen before having gel nails applied. Another option is to wear UV-protective gloves with the fingertips cut off so only the nails are exposed to the light. Users of regular nail polish can try fans or air-drying if they want to avoid the devices.