Wearable tech: sensing when you've had enough sun

Basking in the warm sun is a luxury that many of us love, and it’s also good for you - up to a point - because the ultraviolet rays in sunlight produce the bone-boosting hormone vitamin D in your skin. But too much UV causes sunburn, skin ageing and wrinkles, and it’s a major risk factor for skin cancer, rates of which have more than doubled in recent decades. Now scientists from Australia have come to the rescue with a wearable sensor that you pop on your wrist; it goes blue when you’re past the safe daily sun limit for your skin type. Inventor Vipul Bansal told Tamsin Bell how it works...

Vipul - UV is invisible and it’s not hot so you can’t feel UV, and the heat that we feel in the sun is because of infrared rays, it’s not because of UV. We are trying to make UV sensors in the form of wearable sensors which change colour when you go in the sun. This ink can interact with the UV light and then become blue.

Tamsin - So once our sensor becomes blue we know that we have to go inside?

Vipul - Yes. And this ink can give a warning signal - now it’s time for you to go back in.

Tamsin - How does this work? What chemicals are involved?

Vipul - The two main chemicals in this ink - we call it an invisible ink because it’s initially colourless. There’s a chemical called polyoxometalate that's a big molecule, a lot of phosphorus, oxygen involved. The second component in the ink is lactic acid, a common chemical which is present in yogurt. So when we mix these two components together and we shine this ink with the UV light, the lactic acid molecules can give electrons to the other molecule. When this happens the polyoxometalate becomes blue in colour and that’s what we see.

Tamsin - What about different skin types or UV tolerance, how does this take that into account?

Vipul - We have six different types of skin. It could be very fair skin to very dark skin. Now the UV requirements and the tolerance of these skin types are very very different. The very fair skin cannot tolerate a huge amount of UV; if you look at a darker skin it can tolerate a reasonably large amount of UV, which means that we have to have personalised sensors for different skin colours. So a sensor that would be for very fair skin, it should develop colour very very fast. On the other hand the colour should develop slowly in case of a darker skin, so a person can stay in the UV for a longer period of time.

Tamsin - I’m a bit of sun worshiper. Is this sensor going to tell me that I have to stop sitting in the sun really quickly?

Vipul - A lot of us love sun and we cannot really avoid exposure to sun. We are recommended to use sunscreen with a high SPF number to reduce the amount of UV that is reaching your skin. When you are applying the sunscreen on your skin, you can also apply it on the sensor. It will also reduce the amount of UV that reaches the sensor and the sensor will develop colour slowly.

Tamsin - I suppose the same would apply if someone sat in the shade?

Vipul - Yes, that is true. We call it a cumulative dose. So when they are in the sun then only the sensor will work and depending on the intensity of the sun the sensor will either work faster or slower. And then it won’t go back once you go back into the shade, so in that way the sensor lasts for one day. We see a huge prospect of these sensors because the sensor can allow people to be exposed to the maximum dose possible without causing harm.

Tamsin - Are you planning to make these and sell them in shops, and how much would it cost?

Vipul - We have a very ambitious target to bring it to the market by early 2020. The retail cost would be somewhere around 1 dollar.