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SPF is an everyday essential for healthier and younger-looking skin, whether it comes in a moisturiser, primer or foundation. Better yet, all three! But how exactly does SPF work and how is it measured?
What you can expect: What does SPF stand for? UVA vs UVB: what’s the difference? SPF Calculation: how is sun protection measured? How long does SPF 50 last? What SPF strength do I need? Does SPF stop tanning? Do I need SPF for lips?
It stands for Sun Protection Factor. This factor measures the UVB protection of a product when liberally and evenly applied to the skin. It doesn’t measure UVA protection, which is only shown in the PA system. To get both UVA and UVB protection, look for sun cream with the “Broad Spectrum” label.
The sun emits invisible ultraviolet radiation. This radiation reaches the Earth’s surface and damages our unprotected skin, even on cloudy or rainy days. We divide this ultraviolet radiation into two: ultraviolet A (UVA) and ultraviolet B (UVB).
UVB rays affect the skin’s surface and cause sunburn. This is damage that you can see and feel, but it also makes skin cells act abnormally.
UVA rays penetrate deeper into the skin and damage everything in their path – including the skin’s vital supportive substances that keep it looking young and healthy. Shorter wavelengths of UVA can also cause painful sunburns.
Both UVA and UVB rays have a part in causing skin cancers.
Though UVB rays are responsible for near-instant visible damage (like the redness or deeper skin tones we get from sunburn), UVA rays cause the skin to tan. This is also a sign of damage in every layer of the skin. Both UVA and UVB rays are present outside year round and in all types of weather, but UVA rays can even penetrate glass, including car and office windows.* That is why it’s so important to wear sun cream even if you aren’t outside a lot. Also, remember to always choose products labelled "Broad Spectrum” to get both UVA and UVB protection.
UVB rays are most intense from 10 AM to 4 PM, at high altitudes and in locations closer to the equator. In comparison, UVA rays are present all day long, staying at a fairly constant intensity no matter where you are in the world. At any hour you see daylight, then UVA rays are damaging unprotected skin! There’s no such thing as a safe amount of UV light exposure.
*Some car and office windows have a UV-protective coating but most don’t, so stay safe just in case!
Before we explain how SPF works, you should know that the lab testing that confirms SPF ratings has its limits. This is because it won’t translate to real world situations. The testing is performed on people, but the lab controls the conditions and fixes the intensity of UV light. In the real world, UVB intensity varies and UVA is consistent. It is exactly the shifting intensity of UVB light that impacts how long it will take the skin to burn (turn red or a deeper brown/black) with any sun cream.
Remember, the SPF rating only measures the UVB protection of an SPF product. SPF numbers can also be misleading because the difference in protection gets smaller as the SPF rating increases. So what does SPF 30 mean? And what’s the difference between SPF 30 and 50? Based on regulated testing:
Looking at it another way:
So which is better SPF 30 or 50? The above shows that SPF 30 lets 50% more UVB rays penetrate your skin, compared to SPF 50. If you know that you won't be able to find shade in the midday sun, we recommend a higher SPF 50 along with a hat and UV-rated clothing.
But there’s a trade-off: super high SPF ratings mean an increased chance of sensitised reactions. And if mineral filters are used to reach an SPF rating over 50, aesthetics will likely be compromised (hello, white streaks). Our Advanced Sun Protection Daily Moisturiser SPF 50 contains a blend of five next-generation synthetic UVA & UVB filters tolerable even for sensitive skin, so try it out if you want high sun protection with zero white cast.
Everyone used to think that simple maths was enough: if you know your skin turns pink or begins to deepen in ten minutes of sun exposure without protection, then factor 50 sun cream would provide 500 minutes of protection (10 x 50 = 500). How long does Factor 30 last? 300 minutes. Factor 15 sun cream? 150, and so on.
But no, SPF 50 does not mean 50 minutes or 500 minutes. SPF ratings aren’t just about the amount of time. Actually, the ratings are about the time and the amount of exposure. Exposure takes into location, cloud cover, latitude, season and proximity to reflective surfaces like water, sand and snow.
To sum up, solar energy intensity impacts the amount of UV radiation to skin. Take a look at the below timestamps:
They can all deliver the same intensity of UV radiation!
It depends how long it takes for your skin to change colour (to a red, tanned or deeper skin tone) in unprotected sun exposure. Figure that out by estimation, rather than experimenting with exposure and multiply that time by the SPF rating. This will get a baseline for how long your chosen sun cream can protect your skin under normal conditions.
“Normal conditions” means the amount and intensity of UV light that usually impacts your skin. When you know your skin will be getting more intense and/or prolonged UV exposure, you need to choose sun cream with a higher SPF rating and reapply often. All UV filters break down and become less effective with ongoing exposure to sunlight so reapplying at regular intervals keeps the protection going.
For example, if your skin normally changes colour after 10 minutes of unprotected sun exposure at noon in your back garden in June, and you use a sun cream rated SPF 30, you will get five hours of sun protection (10 minutes x 30 = 300 minutes or 5 hours). If your skin would normally change colour after 20 minutes of sun exposure at 9:00 am in June in your back garden, SPF 30 would grant you 10 hours of protection. But this is only true if you know how to apply sun protection properly and studies show that most people don’t. Everyday people apply much less sun cream compared to what’s used in lab tests, so you are likely not getting the SPF level of protection indicated on the label.
Another great way of enhancing whichever SPF you choose to use is by adding an antioxidant-rich product into your routine. One ingredient to look out for is coffee-fruit extract. This ingredient contains antioxidant compounds known as chlorogenic acids that can reduce the visible effects of sun exposure by stopping the cascade of the redness-triggering damage that UV light causes.
The bottom line is when you know you’ll be outside for longer than usual or when the sun is more intense in your neighbourhood, opt for higher SPF ratings of at least 30 and reapply every 2 hours. Now that you know how the SPF rating in sunscreen works, check out our top tips on sun protection.
There is a chance you can still get a tan when using a broad-spectrum SPF moisturiser. Of course, our end goal shouldn’t be tanned skin – that’s a red flag for skin-damaging inflammation taking place below the surface.
It seems like a high factor, like SPF 50, would be less likely to lead to tanned skin but it doesn’t work like that. The SPF number only links to the level of UVB protection. As you now know, UVB rays aren’t the only ones responsible for skin tanning – that comes more from UVA rays. So to get UVA protection, your SPF must have the “broad spectrum” label.
Also keep in mind that no SPF can 100% stop sun exposure. Even if you think you’re pretty good about applying protection, the data shows that most of us still aren’t using it as liberally as we should be.
Lips need SPF just like the rest of your skin. In fact, protecting your lips from sun exposure is one of the best things you can do to preserve youthful appearance and decrease the risk of lip cancer. Finding an SPF for lips that you like the look and feel of and will be willing to reapply throughout the day is key (remember, eating/drinking will cause your lip product to rub off, taking the protection with it). Just like with face and body sun protection, it’s important that your broad-spectrum lip SPF is rated factor 30 or higher.
Photodermatology, Photoimmunology, and Photomedicine, September 2020, pages 351–356; and May 2020, pages 192-199 Journal of Cutaneous Medicine and Surgery, June 2019, pages 1-13 Clinics in Plastic Surgery, 2016, pages 605-610 Journal of Clinical and Aesthetic Dermatology, February 2015, pages 43-47 Journal of the American Academy of Dermatology, December 2013, pages 867.e1-867.e14 Dermatologic Clinics, July 2014, pages 427-438 The Journal of Clinical and Aesthetic Dermatology, January 2013, pages 16-24; and September 2012, pages 18-23 Indian Journal of Dermatology, September-October 2012, pages 335-342 Journal of the American Academy of Dermatology, May 2008, pages S149-S154 Cancer Causes and Control, 1996, pages 458-463
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