Healthy skin is meant to have a pH between 4.5 and 5.5, making it slightly acidic, and if you're out of range, it's a problem. According to the company, a compromised pH balance can trigger "inflammatory responses," including "dryness, eczema and atopic dermatitis."

Slap the My Skin Track patch onto your forearm, and you'll be able to learn how acidic (or alkaline) your epidermis is within 15 minutes. And, while other systems have been able to do this before, including the donut-shaped Way which we saw in 2015, none can do it so easily, and with such a small volume of sweat.

Once the 15 minutes have elapsed, users need to open the companion app and shoot a picture of the sticker. The dyes inside the device will have changed color, which can be interpreted by the app to give you a picture of your skin health.

Naturally, once you know the situation, you'll be recommended a series of L'Oreal and / or La Roche-Posay products to buy. And, should you want to try one of these, you'll need to buddy up with a La Roche-Posay dermatologist in the US, who will be testing the product before a wider commercial release.

Meanwhile, the My Skin Track UV sensor, shown off this time last year, is now available to buy in Apple stores and on the Apple website for $60.