This is a computer model that was developed by a sunscreen ingredient company, and there’s another famous one called the BASF Sunscreen Simulator. This nifty tool is the DSM Sunscreen Optimizer: So obviously protection isn’t just about the amounts of filters you put into it, because if it was then they’d be done in a day. One cosmetic chemist told me that she just finished formulating a sunscreen, and it took her 6 months, even though she started with an SPF 30 base and just had to raise the SPF. It can take months to finish a sunscreen. The saying that the ingredients list can’t tell you the whole story about how a product works is especially applicable to sunscreens.Ĭosmetic formulators know this really well, because sunscreens are one of the hardest things to formulate. Why can’t you work out the SPF from the ingredients list? So why are we still doing this annoying test? Can’t we work out SPF in other ways? Let’s talk about the issues with alternative methods. There are little differences between the regions with things like how reproducible the test has to be, and how many volunteers you have to use, but in essence the test is the same. This applies to most places worldwide, including the US, South Korea and Australia. So both the international standard test for SPF labelling (the ISO 24444 test) and the FDA test (which is very similar) still use in vivo tests on actual human beings. Sunscreens also dry on skin in a particular way which might be different from drying on glass, or on different types of plastic. Human skin is bumpy and so if you have a thicker sunscreen, then some of it might not get into the grooves and you might have little bits of hills sticking up. But the main issue that keeps coming up is that it’s really hard to mimic how sunscreen reacts with human skin. The sun care industry has been working for a long time to find an alternative way of testing SPF. And you’re harming people with this test. Anything that involves human volunteers is a lot more expensive than if you just have to use a machine – it’s somewhere in the region of $5000 to 10000 USD for a test, and if the first version of your sunscreen doesn’t give you a high enough or consistent enough SPF, then you have to repeat this again and again until you get it. There are a lot of really annoying things about this test. A special UV lamp is shone onto the backs, and how much UV the skin can take with and without the sunscreen is compared. SPF tests are done by putting 2 milligrams per square centimetre of sunscreen on the backs of human volunteers. In short, SPF measures how much protection you get from erythemal or sunburn-causing UV from a sunscreen, or any other product. Related post: What Does SPF Mean? The Science of Sunscreen Let’s start with how SPF testing is done. The video is here on YouTube, keep scrolling for the written version… Hopefully this will give you more insight into the whole situation and why SPF testing is so darn tricky. So were we all wrong to say the labeled SPF was the best data point we had? Should we stop trusting all Korean sunscreens, or Asian sunscreens? Should we only use sunscreens from large Western manufacturers? Why did cosmetic formulators and scientists who understand sunscreen wait till there were two in vivo SPF tests before saying anything? Purito put out a statement saying they’ve paused the sale of their sunscreens, and they said that they actually sent off their sunscreens for a test earlier but they still haven’t gotten the results yet. But I think most people now feel like there is enough evidence to be more cautious. There is the possibility of the newer test being wrong and the label being correct, and I’ll go into some of the possible reasons for this later on. This sort of thing has happened with all sorts of sunscreens from all over the world before, from both big and small brands – where later testing didn’t get the SPF that’s claimed on the label. There were rumours that it didn’t match the label claim before, but until INCI Decoder published the two in-vivo SPF tests on their blog, a lot of scientists were saying that there wasn’t enough evidence yet to disbelieve the label. Recently you might have heard that one of my former favorite sunscreens Purito Centella Unscented Sun tested at SPF 19, which is much lower than its labeled protection of SPF 50+.
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