For years, no matter what I did when sailing, my nose burned. Finally, I figured out that I could coat my skin in thick layers of zinc oxide to keep it from cooking. Of course, the down side to that tactic (as is obvious in the image below) is that I look like an idiot. The trouble with traditional sunscreen is that we often only work out that we need to apply more after we've already been cooked. Sure, we could use timers and alarms on our phones to provide reminders to re-apply but this is tricky because the duration of sunscreen effectiveness varies wildly with location and the intensity of ultraviolet light on a given day. A simple sensor capable of warning when a person is about to be burned would be useful and this is what a team of chemists is reporting that they have accomplished.
The team, led by Justin Gooding at the University of New South Wales in Sydney, focussed their efforts on the compound titanium dioxide. Used widely in sunscreens, titanium dioxide sheds electrons when it gets bombarded by ultraviolet light. These electrons then interact with oxygen and hydrogen in the surrounding environment and create highly energetic particles called free radicals. Dr Gooding speculated that if these free radicals were placed next to some simple food dyes, then the dyes would be degraded and change colour. Most importantly, he guessed that as the titanium dioxide was struck by ever more ultraviolet light, the colour of the dyes would change more noticeably.
To test the idea out, Dr Gooding and his colleagues printed titanium dioxide and a variety of food dyes onto pieces of paper and then blasted them with ultraviolet light to see if they would change colour. This is precisely what happened but, after the team achieved their goal, they realised there was still a problem.
We do not all come in one pigment and different levels of pigmentation result in each of us being able to withstand different amounts of time in the sun before being burned. Keen to be able to build a sunburn sensor that would work for people from all walks of life, the Dr Gooding speculated that he might be able to place an ultraviolet light filter over the sensor to adjust how quickly it changed colour. He tried a bunch of different filters ranging from those that strained out just 1.5% of the ultraviolet light before it hit the film to intense filters intended to emulate very dark skin that blocked 70% of the harmful light. These tactics worked and Dr Gooding is now intending to move his product towards commercial development. Here's hoping it works well enough for me to be able to ditch the zinc oxide and return to clear sun screen that doesn't leave me looking any more foolish than normal.
* And, yeah, there is the added nuisance that if I had my phone on deck it would only be a matter of time before it ended up in the deep blue.