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9 August 2021

SPF, UVA, UVB: sun creams explained

What do UVA and UVB mean in sun creams? How do sun creams work? And how much do you need to apply? All your questions answered.
Which?Editorial team
Sun cream being used on legs

Staying protected in the sun is crucial, and sun cream is an essential part of sun-safe behaviour, alongside seeking shade and covering up. But how do sun creams actually work? How often do you need to apply them? Can you rely on once-a-day sun creams? And what about the SPF in your make-up? 

Find out, and get answers to all your other sun cream questions below.

We've tested sun creams to help you choose effective protection for your family, as well as products that feel great on your skin.

Find the best protection for you – check out our sun cream reviews.

What does SPF mean?

The Sun Protection Factor (SPF) gives an indication of the amount of protection sun creams offer against UVB radiation. It gives an indication of how much longer skin that's covered with the sun cream takes to redden in response to UV, compared with unprotected skin. 

SPF30 is a popular choice among consumers, so we've tested products of this strength, along with SPF50 kids sun screens. Find out which products didn't meet their sun protection claims in our tests, check out our list of Don't Buy sun creams.

What are UVA and UVB?

These are both types of ultraviolet radiation from the sun. Both types have been linked with skin cancer, although UVB is the main cause of sunburn. Sun creams usually also offer some protection against UVA, which has been linked with premature ageing. 

The UVA seal – a logo with ‘UVA’ inside a circle – also indicates that a product protects against UVA. Find out which sun creams passed our UVA and UVB tests using our sun cream reviews.

What does the UVA seal mean?

The UVA seal indicates that a product meets the EU recommendation for sun creams to offer a UVA protection factor equivalent to at least a third of their SPF. However, some products display the Boots star rating – the protection claimed by these products is higher than the minimum required by the EU. 

Some sun creams use other logos, some of which conform to other countries’ standards.

How does sun cream work?

There are two types of active ingredients in sun creams – physical blockers and chemical absorbers. Chemical absorbers soak up UVA and UVB radiation, while physical blockers act as a screen to protect the skin. Many products use combinations of the two.

Does sun cream go out of date?

Yes. Before using a sun cream, check the bottle for a 'period after opening' symbol. Most of the sun creams we've tested say they have a shelf life of either 12 or 18 months after opening. Storing sun cream at high temperatures or in direct sunlight can decrease its shelf life. So if you took last year's sun cream to the beach with you, it may be time to buy a new bottle.

What factor sun cream should I use?

The NHS and Cancer Research UK both recommend you pick a product with an SPF of at least 15, while the British Association of Dermatologists suggests we opt for at least SPF30. If your skin burns easily, it's best to stay on the safe side and opt for a higher SPF.

When should I apply sun cream?

The UV index gives a good indication of whether you need to apply sunscreen on any given day. The index ranges from low (a rating of one or two), to very high (eight and over). If the index is three or greater, it's worth considering using sunscreen – particularly if you burn easily.

A high UV index rating doesn’t always coincide with hot weather – check the rating using the Met Office website.

How often do I need to apply sun cream?

It’s best to first apply sun cream 15 minutes before you head outside. Experts recommend that you then reapply it every two hours, but you may need to reapply it sooner than this if you go swimming or find yourself sweating a lot.

SPF gives an indication of how much longer it will take for your skin to burn with sun cream compared with bare skin over the whole day. However, studies suggest that most people won’t achieve the specified SPF due to poor application – it’s better to apply too much sun cream than too little.

How much sun cream should I apply?

It’s very unlikely you’re applying too much. The World Health Organization (WHO) recommends 35ml for the total body – that’s around seven teaspoons: one for the face/head and neck, one for each arm and each leg, and one each for your front and your back.

The image above shows the average amount of sunscreen we typically apply in a single full-body application in the hand on the left. Next to this – in two hands – is the amount we should be applying.

Not applying enough sun cream reduces the level of protection you'll receive. According to the WHO, applying a smaller quantity of sun cream leads to a disproportionate reduction in protection – if the quantity applied is reduced by half, protection may fall by as much as two thirds.

Find out which provide the most effective protection by browsing our sun cream Best Buys

Once a day sun creams

More and more products are becoming available that claim to provide sun protection for up to 10 hours after a single application. However, when we tested once-a-day sun creams to see if they lasted all day we found worrying results.

Read more in our guidelines on once-a-day sun creams.

Will water resistant sun creams protect me?

It's common for sun creams to claim to be 'water resistant', but keep in mind this doesn't mean that they're waterproof. You may be surprised to learn that the industry guideline for water resistant sun creams allows the SPF of a product to drop by 50% after a total of 40 minutes in water. Water-resistance testing also takes place in what is essentially a bath – using tap water. 

We tested two popular sun creams in chlorinated water (to mimic a swimming pool) and salty water (to mimic the sea). We also added another scenario using fast-moving tap water to see what effect this had. Most of the time the products weren't as effective in our more realistic conditions as they were in tap water. If you're relying on a sun cream at the beach, be careful to apply it copiously before swimming, and again when you leave the water.

Do I need special sun cream for babies?

Sun creams that are specially formulated for children and babies are less likely to irritate young skin. However, sun cream is just one part of staying safe in the sun – encouraging kids to slip on a t-shirt, slop on sun cream, slap on a hat and wrap on sunglasses are all good ways to help them remember to stay safe in the sun. Babies should be kept in the shade.

Learn more in our guide to baby and child sun creams, where you can also see which kid's sun creams passed our tests - and the ones that failed.

Which sun cream should I use if I have sensitive skin or an allergy?

‘Sensitive’ sun creams are available; these tend to use physical blockers, which act as a screen to protect the skin. Chemical absorbers soak up UV radiation but are also more likely to cause skin irritation than physical blockers. There’s a long list of ingredients that are used as chemical absorbers, so it’s easiest to simply look for products that are labelled ‘sensitive’ rather than search for specific ingredients.

How do organic or natural sun creams differ?

‘Organic’ or ‘natural’ sunscreens often use physical blockers, such as titanium dioxide or zinc oxide, to stop UV rays from reaching the skin. Physical blockers are made using naturally occurring minerals. If you do pick a natural product, it’s important to check that it definitely includes an ingredient that acts as a sun filter.

Will make up with SPF protect me?

Some protection is better than nothing, but products will only reach the full SPF when the right amount is applied. For any product to provide the SPF it claims, you need to apply 2mg per cm2 – which means around a teaspoon of product needs to be applied to your face. And, just as with sun cream, it needs to be reapplied regularly. In reality, you’re unlikely to apply the amount of make-up required – in the case of foundation, that would mean a 30ml bottle would only last six applications. When used realistically, make-up isn’t going to protect you from the sun on its own.