Scientists have developed the world’s smallest wearable device – a wafer-thin, feather-light sensor – that can fit on a fingernail and precisely measure a person’s exposure to ultraviolet (UV) light from the sun.

The broader goal is to provide a technology platform that can save lives and reduce skin cancers by allowing individuals, on a personalised level, to modulate their exposure to the sun, researchers said.

The device, as light as a raindrop, is powered by the sun and contains the world’s most sophisticated and accurate UV dosimeter, they said.

The device called UV Sense was unveiled at the Consumer Electronics Show (CES) in Las Vegas.

“We think it provides the most convenient, most accurate way for people to measure sun exposure in a quantitative manner,” said John A Rogers from Northwestern University in the US.

UV Sense has no moving parts, no battery, is waterproof and can be attached to almost any part of the body or clothing, where it continuously measures UV exposure in a unique accumulation mode, researchers said.

Rogers said the device, created in a partnership with L’Oreal, is meant to stick on a thumbnail – a stable, rigid surface that ensures robust device adherence. It is also an optimal location to measure exposure to the sun.

“It also is one of the few sensors that directly measures the most harmful UV rays. Further, it simultaneously records body temperature, which is also very important in the context of sun exposure,” he said.

Users only need to download an app on their smartphone, then swipe the phone over the device to see their exposure to the sun, either for that day or over time. The app can suggest other, less UV-intense times for outdoor activities or give peace of mind to individuals who are concerned about overexposure.

“UV Sense is transformative technology that permits people to receive real-time advice via mobile phone messages when they exceed their daily safe sun limit,” said June K Robinson, research professor at Northwestern University Feinberg School of Medicine.

The researchers have received a USD two million grant from the National Institutes of Health in the US to deploy the fingernail UV sensors in human clinical studies of sun exposure in cohorts of subjects who are at risk for melanoma.

The first pre-pilot field trials launched in December, researchers said.