If you've ever skipped sunscreen on a cloudy day, left a window cracked on a long drive, or assumed the pool was keeping you safe from the sun — you're not alone. These are some of the most common mistakes people make with UV protection, and they're completely understandable. UV radiation is invisible. You can't feel it building up. And the surfaces we assume are protecting us often aren't doing nearly as much as we think.
Here's the science behind three of the biggest UV myths, and what actually keeps your skin safe.
The Cloudy Day Myth: "There's No Sun, So I'm Fine"
This one might be the most widespread misconception in sun protection.
Clouds do block some UV radiation, but how much depends entirely on the type of cloud, its thickness, and how the sun is sitting behind it. Light or scattered clouds barely filter UV at all. In fact, over 90% of UV radiation can pass straight through thin cloud cover. Even on an overcast day, you're typically receiving the majority of the UV dose you'd get under a clear sky.
But here's the part that surprises most people: partially cloudy days can actually be more dangerous than completely clear ones.
When cumulus clouds break up and scatter across the sky, UV rays can reflect off their edges and bounce from multiple directions at once — a phenomenon researchers call cloud enhancement. Studies have recorded UV levels on partially cloudy days running 25–50% higher than a cloudless sky. Some measurements at high-altitude observatories have recorded UVB levels up to 30% above modelled clear-sky predictions.
The reason? On a clear day, UV comes from one direction — the sun. On a scattered cloud day, reflected UV arrives from all angles simultaneously. There's no shade from clouds if the radiation is bouncing around you.
It's also worth understanding why cloud cover fools us so reliably: we use temperature and visible brightness as our UV proxies, and clouds disrupt both. A cool, overcast spring day in Melbourne or London can still carry a UV Index of 3 or higher — the Cancer Council's threshold for recommending sun protection. UV doesn't wait for summer.
The rule of thumb: if you can see your shadow, UV is reaching you.
The Car Window Myth: "I'm Inside, So I'm Protected"
Glass feels like a barrier. And for some UV wavelengths, it genuinely is — but not for all of them.
To understand why, it helps to know that UV radiation comes in two main types that reach the Earth's surface: UVB and UVA. UVB has a shorter wavelength and is primarily responsible for sunburn. UVA has a longer wavelength, penetrates more deeply into the skin, and is the dominant driver of premature ageing and a significant contributor to skin cancer risk.
Standard glass — the kind in most side windows, home windows, and office buildings — blocks UVB almost entirely. But it allows a substantial proportion of UVA to pass straight through.
In cars, the difference between windows is meaningful. Windscreens are typically made from laminated glass for safety reasons, and that lamination happens to also provide effective UVA protection — blocking around 94% of UVA rays. But side windows, rear windows, and sunroofs are often made from standard tempered glass, and research shows the driver's side window can transmit well over 70% of UVA radiation.
For people who spend long hours driving, this adds up. Studies have identified a consistent and measurable pattern: in countries that drive on the right, skin damage, premature ageing, and skin cancer rates are statistically higher on the left side of drivers' faces, necks, and arms — the side closest to the window. In Australia, where we drive on the left, that pattern reverses to the right side.
Long-haul drivers, people who commute daily in sun-exposed directions, and anyone sitting beside a window for hours — at a desk, on a train, in a greenhouse — are accumulating UVA exposure they may not be accounting for.
Window tinting, UV-blocking film, and wearing UPF-rated clothing while driving are all practical ways to manage this. Sunscreen alone is less reliable in this context — most people don't apply it before a commute.
The Water Myth: "I'm In The Pool, The Sun Can't Get Me"
The snorkeller who spent a day floating on the Great Barrier Reef and ended up in hospital with severe burns on the backs of their legs is an extreme example — but it illustrates something important. Water doesn't block UV. It filters some of it, and it cools your skin so you don't feel the damage accumulating.
The numbers are more confronting than most people expect. At just 50cm (roughly knee-depth in a pool), UV intensity is still around 40% of what it is at the surface. At 1 metre, UVA rays — the deeper-penetrating type — remain substantial. Even the reflective surface of the water itself can amplify your exposure by bouncing rays back upward, effectively increasing the UV dose to your face and shoulders by up to 10%.
UVB rays (the sunburn type) are absorbed more quickly by water — they're largely attenuated within the first few metres. But UVA, which causes skin ageing and contributes to long-term cancer risk, penetrates much deeper. In clear ocean water, UVA can reach meaningful depths well beyond where most people are swimming.
The practical implication: if you're in shallow water, at the surface, or floating — you're still receiving significant UV exposure to every part of your body that's near the surface. The fact that you feel cool doesn't mean you're protected. Standard sunscreen washes off faster than most people realise, which is why water-resistant formulas and UPF-rated rash guards and swim shirts are the more reliable defence for extended time in or on the water.
So What Actually Blocks UV?
This is where the science gets useful.
The most reliable UV protection works by creating a physical barrier between radiation and skin — one that doesn't wash off, doesn't depend on reapplication, and doesn't lose effectiveness as the day goes on.
UPF-rated fabric is that barrier. UPF 50+ means less than 2% of UV radiation penetrates the material — regardless of whether it's cloudy, whether you're near water, whether you've been wearing it all day. It doesn't expire. It doesn't sweat off. A UPF 50+ shirt worn on a partially cloudy day, on a boat, or during a long drive covers the exact scenarios where most people's sunscreen routine fails them.
A broad-brim hat rated UPF 50+ extends that protection to the face, neck, and ears — the areas that take the most cumulative UV damage over a lifetime, and the areas most commonly missed by sunscreen application.
This isn't to say sunscreen isn't valuable — it is, especially for areas that can't be covered by clothing. But as a primary defence, it requires perfect execution: the right amount, applied correctly, reapplied on schedule, on every occasion. UPF clothing removes that execution risk.
The Takeaway
UV radiation moves through more barriers than most people assume. Clouds scatter and redirect it. Car windows filter some wavelengths but not others. Water absorbs it gradually but doesn't stop it — and reflects it back from the surface for good measure.
The common thread in all three scenarios is that we rely on things that look like protection, when the radiation itself is invisible and cumulative. The damage from a lifetime of underestimating these moments is real — it shows up as premature ageing, and in Australia especially, in skin cancer statistics that rank among the highest in the world.
Simple, reliable protection — sunscreen, a well-made hat, a UPF 50+ shirt — takes the guesswork out of it. You don't need to check the cloud type, inspect your car's glass specification, or worry about whether you've been in the pool too long. You're covered.
Content disclaimer: The information on this website is for general educational purposes only and is not a substitute for professional medical advice. If you have concerns about UV exposure or skin health, consult a qualified dermatologist or medical professional.