27 Jun 2011

Science Behind Sunscreen - How SPF and Sun Creams Work

This week, The Science Behind Beauty Project is getting ready for the summer! Well if it ever turns up! Even though it's raining, I'm sure some of us have some great holidays planned and will definitely want to know more about sunscreen (especially as our skins will not have gotten used to the sun AT ALL). So let's find out more about your summer essential: sunscreen!


First a little history: the first sunscreen is thought to have been engineered by chemist Franz Greiter in 1939 and was called Gletscher Creme (Glacier Cream). Even though it was probably only a factor 2, it was very popular and is actually the ancestor to the brand Puiz Buin.


How tanning works and the different radiations


 Let's start with some basic physics. The sun emits many different radiations: among them are UV (Ultra-Violet) radiations which as you can see from the light spectrum graph are found at a lower wavelength than visible light. There are different kinds of UV light: UV-A and UV-B (there is also UV-C but let's not overcomplicate things). Now the ozone layer blocks about 97-99% of the radiation coming from the sun but that still leaves a good 1-3% of radiation reaching the Earth's surface and thus our skins.


Tanning mainly involves a component many of you might have already heard of: melanin, which is also present in hair and other areas of the body. Melanin is build within our cells as a defence mechanism against UV radiation. When exposed to radiation, melanin absorbs it and dissipates the energy as heat so it doesn't affect the skin tissue. But different radiations affect melanin differently. Whereas UV-A oxidises melanin already present in the skin cells (oxidation is a process during which a molecule loses some of it's electrons changing many of it's characteristics) and activates the release of more melanin from cells; UV-B stimulates the body to produce more melanin. This means the different rays affect our skin (and our tans) differently: UV-A yields a quick tan while UV-B takes two days or so to affect the skin.


What is sunscreen made of?


Well, bar the usual ingredients a cream requires to be soft and moisturise the skin, there are two those of active ingredients in sunscreen: some that absorb the sun's UV radiation and others that reflect it. Usually the compounds that absorb radiation are organic chemicals and those that reflect and scatter it are inorganic particulate. Some are able to do both: an organic particulate called Tinosorb M. is effective at 90% by absorption and 10% by scattering of UV light. Some other ingredients that are very good at their role: titanium dioxide, zinc oxide, avobenzone and ecansule.


What do the factors mean?


Now this is all very interesting (I hope) but it doesn't help you adequately choose a good sunscreen. Let's look into the three things you should keep your eyes peeled for: SPF, PPD and Star Ratings.


1.  SPF - Sun Protection Factor is a measure of the amount of UV radiation required to cause sunburn in skin without sunscreen on. The equation which gives us the numbers is  rather complex but sufficed to say the higher the factor the more it protects. But be aware, a common misconception is that factors mean then number of hours one can stay in the sun without being burned: this is a myth! Another issue here is that SPF only gives you guidance on protection against UV-B radiation; but as we have seen, UV-A is also a concern.


2. PPD - Persistent Pigmentation Darkening? Never heard of it? I thought as much. PPD measures the amount of the UV-A protection in a cream, something most sunblocks completely ignore or have very little of. Thankfully this is now gaming and maybe creams are now designed to block both types of radiations. Technically speaking, a PPD of 10 should allow 10 times more UV-A exposure than without (not 10 hours).


3. Star rating - Recently set up in the UK and other countries, a star rating is a ratio of UV-A to UV-B protection. Ideally you want a cream with a PPD of at least a third of the SPF. Keep your eyes peeled!


What they don't tell you


Although generally speaking all sunscreens provide protection and are beneficial in the fight against various types of skin cancer, they don't provide what they promise and some forget to mention some important facts.


We have already seen that many sunscreens don't block against UV-A radiation, which can increase the melanoma in your skin leading to different types of skin cancer.


There is also the issue of how long sunscreen is actually affective. A lot of testing is being done into the effects of indirect damage from free radicals and reactive oxygen species; some of which shows that after 60 mins of sun exposure some sunscreens can be more harmful than helpful. Photo-stable filtering systems have been created though which allow a longer solar exposure, look out of ingredients like drometrizole trisiloxan, bisoctrizole or bemotrizonol for better protection.  


Overall the main conundrum surrounding sunscreen (and many other creams) is fairly simple: do these UV filters act ON or IN the skin? Sadly this is something our scientists have yet to find out.


So in the meantime, enjoy the sun responsibility (the same way you enjoy your Pimm's) - make sure you always have sunscreen on and protect any sensitive areas. Look out for sunscreens with both SPF and PPD and a high star rating.... And a nice smell of course!

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4 comments

  1. I thought this was a great post Lauren! Really interesting and informative - i just think there could be a bit more on how the sun affects the skin (rather than just focusing on tanning and the production of melanin) to highlight the need for sunscreen!

    I think a lot of people are still sadly oblivious to the damage the sun can do (and i'm just as guilty as everyone else for not wearing sunscreen when i should) - did you know that some people still think it's a good idea to go on sunbeds before going on holiday to get a "base tan?" There was a blog i read where the girl kept going on about what a great an idea that was - it is actually only proven to give an extra spf of about 4! Even though sunbeds increase the chances of skin cancer by 75 %

    Also i liked your bit on how suncreams might also be harmful - i read another blog about this recently where the person was saying how they don't wear face creams with spf etc. in case they do more harm than good! I'm of the opinion that if you know of a danger you should try to protect yourself - as we know of the danger of the sun and currently don't know sunscreens are dangerous then i'm all for being blissfully ignorant haha!

    Again, love this post and your science posts in general (i'm a not so closet science geek!)

    xxShivvyxx

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  2. P.s. People seriously believe a sun bed could in any way be good. I shudder to think x

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  3. Thanks Shivvy. I wish I could take credit bi this was written by my science correspondent Tash from The Science Informant http://scienceanythingandeverything.blogspot.com/ who is super clever and doing a v hard phd. She writes all (except one) of my science behind beauty articles. Xxx

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  4. [...] Science Behind Sunscreen – How SPF and Sun Creams Work | Lauren ... Science Behind Sunscreen – How SPF and Sun Creams Work. This week, The Science Behind Beauty Project is getting ready for the summer! Well if it ever turns up! Even though it's raining, I'm sure some of us have some great holidays planned and will definitely want to know more about Now the ozone layer blocks about 97-99% of the radiation coming from the sun but that still leaves a good 1-3% of radiation reaching the Earth's surface and thus our skins. [...]

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