The Sun is a Deadly Laser: A User’s Guide to Sunscreen

Any Aussie kid worth their salt knows the ancient proverb: ‘No hat, no play, no school today’.

But for those of you who grew up outside of Australia, or somehow magically always remembered to bring your hat, the saying was an adaption of a school rule that was literally called ‘no hat, no play’. It effectively meant: if you do not have a hat, then you cannot play in the sun.

The saying itself was popularised and propagated by chagrined, hat-less children, who perhaps weren’t the most creative. No awards given for rhyming ‘play’ with ‘today’.

But what even Aussies might not know is that the rule wasn’t originally created for primary schoolers who hadn’t yet learned that the sun is a deadly laser. It was actually a skin cancer prevention program introduced by the charity SunSafe in the 1980s. The same year the iconic Slip, Slop, Slap campaign was introduced. It took until 1998, when the Cancer Council Australia launched SunSmart Schools, for the message of sun-safety to  target, which was probably a fair call. After all, two in every three Australians will get skin cancer in their lifetime. Perhaps a ‘get ‘em while they’re young’ approach is exactly what is needed.

But as one study has shown, we’re not the best with our sun safety knowledge. Yet.

An Introduction to Sunscreen

There are two broad types of sunscreens: physical and chemical. In Australia and America, sunscreens use the SPF rating system, which is a measure of the percentage of UVB rays that are filtered, either reflected or absorbed, depending on their type. The higher the SPF number, the more protection it provides, up to a point. After around SPF 30, there are severe diminishing returns.

In fact, SPF 30 is a good example – it is around 97% effective at blocking UVB rays while SPF 60 is 98% effective. Double the figure, more expensive, a 1% difference #notworththeextracoin. Although, in recent years, there has been a push to focus less on the amount of UVB that is blocked, and more on the amount that penetrates, because that’s what’s actually damaging the skin. From this perspective, instead of a 3% penetration rate, it’s 2% instead – a 50% reduction. Whether or not you see it that way is up to you. 

But that’s not the be-all-and-end-all of sunscreen, because it’s a surprisingly complicated topic. For starters, the SPF system only regulates UVB protection, not UVA. Even though both are types of Ultraviolet radiation that damage the skin, just in different ways.


UVB is responsible for that classic lobster-like appearance you get after a few hours (or minutes) in the sun and is thought to cause most types of skin cancers. But thankfully, UVB isn’t some kind of omnipresent monster. The level of UVB in an area depends on a variety of factors. The season, time of day, distance from the equator, and altitude, are just a few of them.

Because UVB is so situation dependent, it’s hard to understand on a day-to-day basis. That’s why the UV Index was invented. It’s a 5-point scale, from low to extreme, that measures UVB radiation intensity. On the low end of the scale, 1-2, sun protection isn’t needed. Once the forecast gets above 3, the Cancer Council generally recommends you Slip, Slop, Slap on some protection.

The good thing about the UV Index is that it’s easily represented in a visual format. This is important because UV can’t be seen or felt, so many misconceptions have been formed about it – like that it’s based on temperature, something one in four people believe. Daily forecasts that the average person can read challenge this idea.


And because the UV Index is based on real-time information, updated on a minute by minute basis, it is far more accurate than just prediction. This is because it takes into account factors which mitigate and exacerbate the effect of UVB. In an ideal scenario, we would see a perfect bell curve of expected UV throughout the day. But things are never that simple. For starters, UV can be reflected on surfaces like water, sand, snow, pavement and glass, which leads to an increase in UV exposure. Even clouds, which can sometimes block some UV from reaching us, can also reflect it, leading to increased exposure. 

For those DataIsBeautiful nerds, the UV Index can also be used to compare how ‘at risk’ a place is on average over a longer period of time based on its geographic location.








The reason UVA isn’t included in the UV index, (ignoring the fact that it was developed at a time when we didn’t fully understand how damaging it was to our skin), is that UVA is omnipresent. If the sun is up, UVA is out. It doesn’t matter the season you’re in, or where you live in the world. UVA accounts for around 95% of the UV that reaches the Earth’s surface, is 30 to 50 times more prevalent, and can even penetrate through glass windows, unlike UVB. Historically, it was thought of as the ‘vanity’ ray, because it is responsible for tanning, hyperpigmentation and wrinkles, but studies over the past few years have shown something more sinister. Although for the record, they definitely do cause those as well.

UVA penetrates far deeper into the skin than UVB does, which is how they actually damage the collagen used to keep skin elastic. As much as 80% of premature skin ageing, most famously wrinkles, is due to UV exposure. But more worryingly, because UVA can delve so deeply into the skin, they can also damage keratinocytes, cells which reside in the basal layer of the epidermis – where most skin cancers occur. And newer research has shown that, at the very least, UVA contributes to the development of skin cancers and may even be what initiates them.

But like all dichotomies, this too is false. It is over simplified. Neither UVA nor UVB work independently of one another. They’re both responsible for damaging the skin, causing wrinkles, and risking cancer. There are no safe UV rays. Which is why we need to be protected against both.

Broad Spectrum

This is where ‘Broad Spectrum’ sunscreens come in. Protecting from both UVA and UVB rays, this is what you should be looking for when buying sunscreen. But in a 2015 study that tested consumer knowledge of sunscreen labels, only 34.2% of respondents listed it as an important factor in their purchasing decision, instead prioritising SPF. This led researchers to come to the conclusion that consumers generally over-rely on the SPF rating, and have difficulty understanding sunscreen labels.

How Sunscreen is Measured


In saying that, there is another, often overlooked, facet to mastering the art of sunscreen: applying enough. It may sound simple, but people typically only apply about ¼ of the amount they should to get the advertised SPF value.

In order to get reliable, reproducible results, the standard amount of SPF for testing is 2 milligrams of sunscreen per centimetre of skin (2 mg/cm²), which translates to around 30-35 ml for an adult body. For reference, that’s about an average-sized bottle of liquid foundation. And get this, you have to reapply it, at least, every two hours. Which, no, people don’t do.

So then, if people aren’t using sunscreen as intended, let’s look at a more pragmatic approach to sunscreen.

Sunscreen in the Real World

Which, in a world-first, is actually better in practice than in theory. Anyone with a background in physics would expect protection to decrease exponentially with less sunscreen, thanks to something called the Beer-Lambert law. But thankfully, this doesn’t seem to be the case.

And instead, a linear relationship has been observed. This more or less means that you’ll get about as much protection as you apply – if you apply 50% of the sunscreen you should, then you’ll get around 50% of the protection.

This shift from an exponential to a linear relationship has a very important implication for real life use. It’s so obvious that it sounds dumb: using some sunscreen is better than none. Nevertheless, it is important to acknowledge, as so few people are meeting the magical standard of one full bottle of Fit Me foundation every two hours.

The Takeaway

It is time we all realise the capabilities, and limits, of sunscreen. Technically, yes, you could use sunscreen as it is prescribed. But quite frankly it’d be an expensive, circuitous, and sticky way of getting the desired result: less UV exposure. What people often forget is that sunscreen is the last line of defence against the sun, not the first. Try to limit your sun exposure – protect yourself with clothing and stay in the shade if you can. But on those days when you know you’ll be basking in the sun, or even if you just want to make sure you’re being 100% safe, wear sunscreen. Your future self will thank you. 


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