The science of sunbathing

Looking out my window right now I can see some blue peeking through the clouds, the temperature is above 10ºC and my calendar tells me it is the end of May. Therefore it is officially the great British summer. Instagram is already filling up with images of barbeques, tents and people pretending to like salad, which means it must nearly be time for some sunbathing! From sun cream to mossie bites (next post) to prolonging your tan – I have used science to get your summer sorted.

Look how good at sunbathing I am...
I am clearly a sunbathing expert…

The science behind how sun cream works:

Sun cream contains a whole cocktail of chemicals that prevent the suns UV radiation from sinking into our skin and causing damage. These include inorganic chemicals like titanium dioxide and zinc oxide, which literally create a barrier layer on the skin and reflect off the UV waves, scattering them away from the skin. The organic chemicals work differently; their chemical bonds absorb the UV radiation, and then release the energy as heat. The list of chemicals on the back of the bottle is pretty long, this is because using a wide range of organic chemicals means there is a variety of bond lengths, so the full range of UVA and UVB wavelengths can be absorbed – this maximises the protection. These organic chemicals do eventually break down after absorbing lots of UV radiation, that’s why you have to reapply sun cream regularly to avoid burning, (and you really don’t want to burn – particularly on your thighs/bum the day before zip lining – new levels of pain).

How to prolong your tan:

When our skin tans, particular pigments in the top layer are activated. Skin cells are in a constant cycle of renewal, so when the pigmented cells on the top layer turnover (old ones die, new ones made) the tan will fade. The cycle of skin cell renewal lasts around 10 days so in theory your tan could be gone just over a week after returning from holiday. A fading tan makes me so sad, so I looked at ways of clinging on to the colour.

One way to ensure a longer lasting tan is to prevent yourself from burning. This is because the burnt skin is damaged so it will regenerate really quickly, causing you to peel – not a good look. Another idea is that if you exfoliate your skin before a holiday, the cells will be at the beginning of the cell cycle when you start to tan, so in theory the tan should last longer. I have personally found this quite effective. Another idea is to moisturise like your life depends on it, this hydrates the skin cells which extends their life. As your skin is hydrated from the inside too it is a good idea to drink loads of water to help fight the fade.

Sunbathing can be as addictive as heroin:

A study from Harvard has looked at how addictive sunbathing can be and the results are a tad scary. Sunbathing was found to release endorphins, which are the same happy hormones released when we exercise to give us that feel-good buzz. This natural high feels so good that our body begins to crave it, the same way that an addict would crave a high from drugs. This is an issue because as you probably know, too much sun can dramatically increase your risk of skin cancer. This is why we need to tan with care, tanorexia is a recognised addiction and it is becoming increasingly common.

By the time you’ve read this, the British summer is probably nearly over, so you better quickly share this and get outside before the rain comes back.

Till next time,




Is an invisibility cloak really possible?

This is a really cool guest blog by the awesome Jonny Brooks!

Have you had a moment so embarrassing that you just wanted the ground to swallow you up? Or you’ve ever wanted to sneak into a room where you know your boss or teacher is talking about you, just so you know what they really say about you? At times like these it would be so handy to have an invisibility cloak just like Harry Potter so no one would ever know you were there.

Well this is what scientists around the world are trying to do right now.

Figure 1: Harry Potter and his awesome invisibility cloak........... that you can't see
Figure 1: Harry Potter and his awesome invisibility cloak……….. that you can’t see

How does it work?

To be invisible you have to make sure that no one can see you. Obvious right? But that’s not the only thing (otherwise hiding behind the door would make you “invisible”). In addition to not being able to see you, the tricky part is also making sure that the person can see what’s behind you. This creates the illusion that people can see straight through the invisible object.

This can be done in several ways, although two of the most common methods are by transformation-optics cloaking and optical camouflage:

transformation-optics cloaking – This method makes use of materials known as metamaterials. These metamaterials are engineered so they exhibit properties that have not yet been found in nature. Built correctly, these materials allow us to bend light around an object making the object invisible and also making sure people can see what’s behind you.

Figure 2: Bending light around an object
Figure 2: Bending light around an object

optical camouflage – This is one of the simpler methods of making an object invisible. Take an object that you want to make invisible (like a human for example) and put a camera on the back of the object. This camera records the images behind the object. If that camera is connected to a video feed in front of the object, then you can project the images of the camera onto the object, creating the illusion that you can see right through it.

Are we close?

Good question. I guess the answer is “kind of”.  Transformation-optics cloaking was one of the first successful demonstration of the method in 2006, but it only worked with microwaves. This means that if our eyes were able to see microwaves, then we would have an invisibility cloak. Unfortunately this isn’t the case. Our eyes see visible light.

Not only that, but many of the methods used to make objects invisible scatter more light, at a different part of the light spectrum, than the object that they were trying to hide. For example, if you had a cloak that made an object invisible to red light, it may actually be scattering lots of blue light. Therefore it may be invisible to red light but if you shine blue light at it, then the object was probably more obvious than it was before.

Despite this, new methods of cloaking are being developed that use electricity to make an object appear invisible. These have the benefit that the device will not scatter light over a broad range of the light spectrum. However, much more research is needed before we have something that truly works for visible light.

So in short, it’ll be a very long while before we have a true Harry Potter style invisibility cloak, but we are making progress. For now, we’ll just have to keep dreaming.

Thanks for writing for Sparkly Science Jonny!

Give him a follow on twitter @Jonny_CBB and check out the work he does at the University of Oxford