L'Oreal unveils super-thin smart skin patch

However, the wearer must take a photo of it and then upload it to an app to see the results.

It has been developed by the firm's tech incubator department, which is a team of 25 scientists and researchers working in several cities around the world, including New York, Paris and Singapore.

The My UV Patch, which is thinner than a plaster and lasts around five days, is disposable and it can be worn on any part of the body.

"Today all the wearables you see are jewellery or wrist bands - but not wearable in the sense that you wear them anywhere on your body," Guive Balooch global vice president of L'Oréal's Technology Incubator, told the BBC.

"Being able to have this technology to measure properties of the skin in real life anywhere you want allows us to develop really new testing methods for future products."

While there are other devices on the market for measuring UV exposure, L'Oreal believes this is the first example of a flexible wearable. "Stickers on the market today go from white to blue in minutes, and then that's it," he said. "You can use ours for days and days."

However, Mr Balooch cautioned that the patch was not intended as a reminder to re-apply suncream. "The issue is not when to reapply, the issue is how much exposure do I have," he said.

The idea is a "pretty amazing" one according to Carolina Milanesi, chief of research at the KWP Comtech research firm. However, Mrs Milanesi added that the need to keep taking pictures of the patch might become frustrating for customers. "I wonder if rather than seeing the cumulative impact in an app I would prefer to be alerted when my UV exposure will cause sun burn or worse," she commented.