Top Dermatologists Answer All Your Questions About Sunscreen

Photographed by Meg O'Donnell.
Regardless of whether you use exfoliating acids or retinol in your skincare routine, wearing sunscreen during the day – and all year round, including in the winter – is a must.
When the sun is shining (and even when it's not), the UV rays emitted have the ability to cause irreversible damage to skin. UVB rays are responsible for sunburn and skin cancer, while UVA rays cause things like fine lines, wrinkles and pigmentation. As well as covering up or avoiding the sun, sunscreen provides a shield against both forms of harmful rays. But while many of us are now coming round to the notion that it's important to apply sunscreen daily, there are many unanswered questions.
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For instance, should you apply sunscreen before or after moisturiser? And is sunscreen in makeup ever enough protection? Ahead, Dr Emma Wedgeworth, consultant dermatologist and British Skin Foundation spokesperson, and Dr Firas Al-Niaimi, dermatologist and Group Medical Director of Sk:n, solve the most common sunscreen queries.
What’s the difference between mineral and chemical sunscreen?
"Chemical sunscreens work like a sponge, absorbing UV light so that it doesn't cause damage to the skin cells," explains Dr Wedgeworth. "Mineral sunscreens (which are currently zinc oxide and titanium dioxide) absorb but also reflect light off the skin."
It all comes down to personal preference when deciding which of the two works best for you. Those with darker skin tones may find that chemical variations will leave behind less of a white cast than mineral types, but there are many suitable mineral sunscreens out there, too.
Should you reapply sunscreen throughout the day? If so, when – and how much?
Reapplying sunscreen all depends on what you are doing, according to Dr Wedgeworth. "If you are out and about and in direct sunlight, you should be reapplying sunscreen every 2-3 hours. We generally advise about a teaspoon amount for the face and the neck. If you are sitting in an office all day, I generally just advise once per day."
What does each SPF factor number mean?
15, 25, 30, 50... Wherever you shop sunscreen, there will always be a number following 'SPF' on each label, but what exactly is this an indication of?
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"SPF or 'sun protection factor' tells us how much longer we can stay out in the sun without burning, compared to our natural protection," says Dr Wedgeworth. "However, the SPF is calculated in laboratory conditions, so it relies on the fact that we put on about 30ml per application and that we reapply regularly." And as Dr Wedgeworth mentioned, it's especially important to reapply sunscreen if you're spending prolonged time in the sun.
What does 'broad spectrum' mean?
You should also see the phrase 'broad spectrum' on the label of any good bottle of sunscreen and it's just as important as the SPF number, if not more so. "A broad spectrum sunscreen protects against both UVB and UVA," explains Dr Wedgeworth. Rays that come from the sun fall into a number of different wavelengths. The SPF on the bottle mainly gives us information about UVB, which is the wavelength of light which causes burning and is responsible for skin cancers. We know that other wavelengths of light, particularly UVA, are detrimental to the skin, causing ageing and wrinkling."
Other wavelengths like infrared and visible light are also being studied.
Should you apply sunscreen before or after moisturiser?
We've established that applying SPF in the morning is a must, regardless of how lengthy your morning routine currently is, but where it features in that routine is especially important. "You should always apply sunscreen after moisturiser," explains Dr Wedgeworth. "It should be the last step in your skincare routine, just before you put your makeup on."
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This instantly maximises your protection against the sun. If you have very oily or acne-prone skin, some experts suggest ditching moisturiser and just applying sunscreen, as most formulas are already suspended in a moisturising base.
Should you put sunscreen on your lips?
A recent survey by EOS revealed that 52% of women think about applying SPF to their lips, with 23% saying they don’t feel it’s necessary. This couldn't be further from the truth, according to Dr Al-Niaimi.
"Some parts of the body are more prone to skin cancers, such as the lips, simply because the skin is thin and they get long-term exposure to sun. It is important to apply an SPF to protect them from UV rays. The sun also completely dries skin (especially lips) out, so moisturising after exposure will give your skin the hydration it needs to repair itself. As well as making sure your lips are protected, it’s also really important to use suncream on a daily basis, even when it’s cloudy."
Is the sunscreen in makeup or moisturiser enough protection against the sun?
Moisturiser and makeup containing SPF may sound smart, but the the simple answer is no, according to Dr Wedgeworth. "We know that you need to apply about 5ml of product to get the required SPF on the bottle and this is much more than most people would use as foundation or moisturiser. In addition, the sunscreens added to makeup may not be the best broad spectrum cover." That said, Dr Wedgeworth recommends a well-formulated tinted sunscreen. "This can be a great base as well as having dedicated SPF technology," adds Dr Wedgeworth.
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Is SPF factor 30 just as strong as factor 50?
"No," according to Dr Wedgeworth, who recommends going for the highest SPF possible. "We know that there may not be huge differences in protection between factor 30 and 50, but this is based on studies under laboratory conditions. Given that we know that most of us don't apply enough or reapply often enough, I think using the highest protection possible is important."
New research found that chemicals in sunscreen can be absorbed into the blood stream. Is this true?
We've established that when it comes to chemicals (and according to the experts, everything is fundamentally a chemical, including water), it's the dose that makes the poison. Dr Wedgeworth agrees. "I think on balance, sunscreen is very positive and safe. It is unlikely that most of us use enough sunscreen for it to be absorbed into our blood stream." And the positives outweigh any potential negatives. "We know from a number of different studies that sunscreen usage reduces the risk of skin cancer," she explains.
What’s the best way to apply sunscreen to make sure everything is evenly covered?
According to the pros, measurements matter and applying sunscreen too thinly could be dangerous. "A teaspoon amount for the face and a 30ml shot glass for the body is ample," says Dr Wedgeworth. "Apply this systematically to each segment of your body and get into your own routine so that you ensure you don't miss any areas."
Is sunscreen that helps you tan a con?
There has been a lot of talk about sunscreen which contains DHA, with some experts arguing that combining the two reduces the efficacy of the SPF. Dr Wedgeworth adds: "I think the problem with fake tan containing sunscreens is that it can be messy and impractical, particularly in direct sunlight. It may be okay if you are using your daily SPF product in the morning on a small area, but for the whole body, I don't recommend this."
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