UVA, UVB, & SPF: What's the difference?

We all know to wear sunscreen... but how does it work? And what exactly does it protect against?  

It doesn’t have to be a hot day for the sun’s UV rays to reach us, and we need different protection for its different types.  

We’ll find out the difference between UVA and UVB rays, plus the meaning of the SPF number you see on the bottle.¹ 

What is it? 

UVA makes up about 95% of all UV light from the sun.² 

It’s also found in sunbeds, sunlamps, and tanning booths. It is not safer to use these than to go out in the sun. In fact, it may be even more dangerous, depending on a few factors like:³ 

• The strength of the UV rays 

• How often you use a sunbed, sunlamp, or tanning booth 

• How long you spend in there 

• Your skin type and colour 

• Your age 

UVA rays penetrate deep into the skin and affect its elastin, so they’re the kind most associated with signs of skin ageing like wrinkles.⁴ ⁵ 

Not all sunscreens protect against UVA light, so it’s very important you find one that does.  

The SPF rating on a sun lotion or suncream does not show its protection against UVA rays. Instead, look for a “star” rating on the bottle.  

The more stars the better; the highest number is 5. You should choose a product with at least 4 stars to help protect you against UVA damage.⁶ 

You might also see a circle with “UVA” in the middle; this means that the sunscreen meets the EU standard for UVA protection.  

As well as wearing sunscreen, you should follow other sun safety measures, like: 

• Staying hydrated: the NHS usually recommends 6-8 glasses (1.5-2 litres) of fluid per day, but advises at least 2 litres during hot weather.⁷ ⁸ 

• Avoiding the sun during the hottest hours of the day (11am-3pm)⁹ 

• Wearing light-coloured, loose clothing ⁹ 

What is it? 

UVB makes up the remaining UV light that reaches us. The rays don’t penetrate as deeply as UVA, but they can still harm our skin.

All sunscreens with an SPF rating will help protect you against UVB rays. That said, no amount of sunscreen can completely block out UV rays of any kind. You’ll also need to follow sun safety guidelines to stay as safe as possible.  

The NHS recommends you use an SPF of at least 30 to help protect against UVB.⁶ 

UV rays can reach us all year round – not just when it’s hot and sunny – so it’s best to wear an SPF no matter the weather. 

SPF stands for “sun protection factor”.  

The SPF rating on a sunscreen describes its level of UVB protection. The higher the number, the more protection it provides. 

The number on the bottle shows you how much longer you’re protected with the sunscreen than without. For example, wearing an SPF 30 would take you 30 times longer to burn than if you didn’t wear any.¹⁰ 

That also means that SPF 30 (when applied correctly) should protect you for twice as long as SPF 15.  

Of course, this is with perfect use – we all sweat, miss bits, or forget to top up our sunscreen. And no sunscreen can block out UV rays entirely. SPF 30 blocks about 97% of UVB, while SPF 50 blocks about 98%.² 

But the higher the number, the better: at least 30 is ideal.  

Know your UVA from your UVB? 

Remember, the sun emits UV rays all year round, so be sure to pick a sunscreen that protects you whatever the weather. 

It’ll become a habit before you know it, so say hello to safer skin!