Brief exposure after a manicure would require multiple visits for potential DNA damage and the risk of cancer with the usage of higher wattage ultra violet (UV) lamps at nail salons

The authors tested 17 light units from 16 salons with a wide range of bulbs, wattage and irradiance emitted by each device for their research letter.
Higher-wattage light sources were correlated with higher UV-A irradiance emitted.
"Our data suggest that, even with numerous exposures, the risk for carcinogensis, remains small. That said, we concur with previous authors in recommending use of physical blocking sunscreens or UV-A protective gloves to limit the risk of carcinogenesis and photoaging."
Source-Eurekalert