All your sun cream and SPF questions, answered

Posted by
Elizabeth Bennett
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A dermatologist answers your SPF queries, plus our edit of the best sun creams for every skin type. 

When it comes to keeping safe in the sun, we all know that SPF is crucial as a means of protecting the skin from cancer, preventing ageing and avoiding a lobster-like complexion

However, when you consider just how overwhelming the sunscreen aisle can be and how much choice there is available nowadays, it’s no surprise that it can a difficult market to shop. From what certain words and phrases on the bottles mean to knowing exactly what product will work under make-up or which ones are suitable to reapply throughout the day over it, or any other of the 1001 questions we all no doubt have, identifying the right product for you, and how to use it correctly, can be a total minefield. 

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So, to help solve all of our SPF woes once and for all - and to answer a few of the most-asked questions, we quizzed dermatologist and founder of skin clinic Eudelo, Dr Stefanie Williams.

What does SPF mean?

SPF stands for ‘sun protection factor’. Although SPF is more accurately defined as the ‘sun burn protection factor’, as SPF only tells us about protection from UVB rays, and doesn’t take into account UVA protection.

What is the difference between UVB and UVA rays?

Both are types of UV light and the easiest way to remember the difference is that UVB = burning and UVA = ageing. Put simply, UVB rays damage the top layer of the skin (hence the burning and redness) while UVA rays penetrate much deeper. Both are dangerous in terms of skin cancer and you need to ensure you’re protecting your skin against both.

How do I know what factor I need?

The SPF number represents how many more times skin will be able to stay the sun before it burns (i.e. protection against UVB rays). For example, if you were wearing SPF15 you would would be protected for 150 minutes longer than if you weren’t wearing anything.

In theory, SPF 15 absorbs 93% of UVB, SPF 30 absorbs 97% and SPF 50 absorbs 98% if applied evenly and frequently. SPFs are rated on a scale of 6-50+ based on the level of protection they offer, with ratings between 6 - 10 forming the least protected end of the spectrum and a rating of 50+ offering the strongest form of UVB protection. 

Products with an SPF below 6 cannot be labelled as sun cream product under EU regulations, as in order for a product to make a sun cream claim, there should be a certain minimum degree of protection against UV radiation. It is generally advised to choose a product between SPF 30 and 50 making sure it also comes with sufficient UVA protection.

How do chemical and physical sun creams work differently?

Physical sun creams act like a mirror and reflect the UV light before it enters the skin while chemical sun creams use chemical filters to convert the absorbed UV light into a safe infrared light.

How much sun cream should I use and how often should I reapply?

You should apply a thick layer of 2mg cream per square centimetre of skin every two hours (which, according to NHS advice equates to around two teaspoons for the head, arms and neck, or two tablespoons if you’re covering your body while wearing a swimming costume).

Research has confirmed that we tend to apply less than half the recommended amount. Subsequently, in daily life we hardly ever reach the SPF factor stated on the packaging which means the theoretical UV absorption rates often plummet.

Does a foundation or moisturiser with SPF offer full protection?

If the product comes with a SPF factor then technically it offers the same protection as a sun cream. However, the issue with just using a foundation or moisturiser is that many only contain UVB protection and not UVA. 

Similarly, it is highly unlikely that you would apply and reapply the foundation or moisturiser at the correct rate to provide sufficient protection.

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What are the most common mistakes people make with SPF?

In daily use we tend to vastly underestimate the amount we really need to achieve the SPF stated on the pack. The other reason is that in order to keep the protection factor up, we need to reapply every 2 hours (and after sweating and swimming), something else many people don’t do. Also, if you notice your skin getting red, it’s too late already, so never ever let it come to that. 

The redness comes with a delay and the maximum redness will only become visible after 24 hours. So if you notice your skin getting red, get out of the sun as soon as you can, as the worst is still to come.

Does sun cream expire?

Every formula has its own expiration date and the majority will come with an expiry date but if not it’s best to get rid of it after a year. If you notice any change to the texture (for example separation) or the smell, it might be better to throw it out earlier.

How do I find a sunscreen that won’t block my pores or give me spots?

Unfortunately many sun protection creams are pore-clogging, even if though they say they are ‘non-comedogenic’. That’s why it’s very important for acne sufferers to choose their sun protection products wisely. While in the past most sun creams came with a rather greasy consistency, today there are advanced, high SPF sun protection products available that have a lovely, lightweight base formulation and will not aggravate your acne. 

See our favourites below.

Do you need to wear SPF in the winter?

We have to make sure to protect ourselves not only from burning on holiday but also from chronic low-level exposure. I always recommend to all of my patients to wear SPF 30-50 all year round. UVA rays do not fluctuate as much throughout the seasons as UVB does so you might not have the warning sign of burning but they are still damaging your skin. 

Both lower-level incidental sun exposure (like going shopping or commuting to the office) and episodically stronger sun exposure (like a sunny holiday) are contributing to skin damage, including premature skin ageing and increased risk of skin cancer.

What about Vitamin D?

The sun stimulates our skin to synthesize vitamin D naturally and good vitamin D levels are important for both physical and psychological health. My best advice is to have a blood test to check your vitamin D level. A simple over-the-counter vitamin D3 supplement can remedy any deficiency without compromising on sun protection for our skin’s health and beauty.

How long does sunscreen last once it’s opened?

Generally, SPF has a shelf life of 2-3 years if it’s stored in a cool place of the sunlight, and if it’s really from last year, then it should be OK. However, do you know how long it has been standing on that local chemist’s shelf? I personally prefer to buy a fresh one every time I go on holiday. Also, you should use sun screen every single day, in which case you would need a new one every couple of months anyway. But regardless of everything else: make sure you check the expiry date on the tube and don’t use it beyond that.

What is the best SPF to use so I can tan without burning? 

A tan (especially in fair skinned people) is in fact a sign that the skin’s DNA has been damaged, so it should be avoided at any cost. Ideally, I like my patients to come back from holiday the same colour they had before they went. 

If I had to give my younger self one piece of advice it would be to embrace my pale skin and not even try to tan. When I think of of all those hours I spent desperately trying to get a tan on teenage holidays (and on occasion even, via indoor tanning beds) it makes me want to cry out, “don’t do it - it’s not worth it!”

Check out our favourite SPF products below

Main image: Unsplash / Yoann Boyer


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Elizabeth Bennett

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