8 Things Your Doctor Wishes You Knew About SPF

​Sunscreen's a bit like the Internet. Most of us have a vague grasp of how it works, but if we were pushed, we couldn't quite explain what the finer points are, and exactly why it fails.

Just like we know you have to be connected to WiFi to hit up Facebook, we know that a high factor sunscreen is a beach day must-have - but to be honest, it gets a bit fuzzy after that point. Like, how can someone actually see when you're typing on WhatsApp? And how does livestreaming really work? Sorry, back to sunscreen.

We rounded up a few top skin experts to bust some myths about sunscreen and get to the bottom of how you can really stay safe this summer. Prepare to be amazed...

1.  There's a difference between UVA and UVB

The sun doesn't just emit one kind of nasty kind of radiation. Here's what it means. Cosmetic doctor Liesel Holler told us, 'The sun emits ultraviolet radiation in the form of UVA and UVB. UVB are the burning rays that damage the superficial layers of the skin causing sunburn. These are the ones you can thank when you're in agony trying to put your bra strap on your bright red shoulders. They also play a key role in the development of skin cancer."

UVA rays penetrate your skin much deeper, causing skin ageing and DNA damage, which leads to skin cancer. "In the past, UVA was considered less harmful than UVB (which causes direct DNA damage), but today UVA is known to contribute to skin cancer via indirect DNA damage. Several studies suggest that the absence of UVA filters may be the cause of the higher incidence of melanoma found in sunscreen users compared to non-users."

2.  So you need a 'broad spectrum' sunscreen

"SPF is a measure of how well a sunscreen will protect skin from those UVB rays," said Dr Dehaven, Clinical Director of iS Clinical. But SPF gives no indication of the level of all-important UVA protection. For that you need to look at the UVA star system, which should be on the back of your bottle. These stars (ranging from 0-5) will tell you the percentage of UVA radiation absorbed by your sunscreen. The British Association of Dermatologists states that a SPF30 sunscreen with UVA rating of 4-5 stars is considered a good standard of sun protection. 

3.   A higher factor doesn't always mean higher protection 

Always reach for factor one billion and feel smug? Think again. "Sunscreens with really high SPFs, such as SPF 75 or SPF 100, do not offer significantly greater protection than SPF 30 and mislead people into thinking they have more protection than they actually do. In fact, SPF30 blocks 97% of UVB rays and SPF50 blocks 98%," added Dr Dehaven.

4.   Fake tan and SPF don't mix

If you've ever been tempted by those miraculous-sounding products that claim to fake tan while they protect, listen up. Abi Cleeve, managing director of suncare brand Ultrasun explains, "The primary ingredient in self tanning products is a chemical called Dihydroxyacetone (DHA). DHA works by creating a chemical reaction on your skin (which turns you that delightful shade of builders brew)."

"DHA is such a strong chemical it attacks other chemicals it's formulated with. If you were to formulate a broad-spectrum sunscreen and put DHA in there, it would leave the factory and pass all tests. It would have its SPF and it would have its UVA but over 2-3 weeks that DHA would destroy the UVA protection." 

"If you're marketing a product as a fake tan but you add an SPF, you don't even have to bother with the UVA because you're not marketing it as sun protection. It's being marketed as fake tan with an added benefit." 

So what to do if you can't bear those first few days looking like Edward Cullen? Fake tan the night before, or a couple of days before your holiday. As long as you don't fake tan on the same day, your regular broad-spectrum sunscreen will work just fine. 

5.   'Photostability' is a thing

If you didn't already feel like you were back in GCSE Chemistry, you will now. Photostability refers to a product's ability to not break down in the sun - so if something's photostable, it shouldn't break down. But that doesn't mean you only need to apply it once: "It still needs to be reapplied because there are other factors involved." That's Dr Marko Lens a plastic and reconstructive surgeon specialising in skin cancer telling me that my Mum was always right.

So what are these other factors? "You swim, you shower, and you towel-dry, all of which remove your sunscreen." Yep, but what if you just lie, inert with a Margarita in one hand? "You sweat".

Basically there is no getting away with it. You need to reapply every two hours, every 30 minutes if you're in hot, humid conditions (so Mexico, Hawaii, the Far East). And by the way…even if it says your sunscreen is 'water resistant' on the label, you have 40 minutes of protection once you're wet. You've been warned.

6.   Spray sunscreens aren't always so hot

With most of our childhood beach memories involving being plastered in gloopy white cream, spray sunscreens sound like a godsend. However, aerosol sunscreens contain a lot of alcohol, which, says Dr Marko "breaks down photostability and dries out your skin just when you need hydration most". Avoiding it altogether in sunscreen is almost impossible. Just stear clear of products that feature alcohol among the first few ingredients in the formula (unless it's a San Miguel bottle) and check the label when it comes to aerosols, gels and anything that claims to be 'cooling'. 

7. Tan-optimising supplements might do more harm than good

Tan-boosting pills are often touted as pre-holiday cheat's way of ensuring a bronzed glow. "I don't see the point of increasing melanin production, which is actually a sign of skin damage. It doesn't make any sense to me", said Dr Marko, and if it doesn't make any sense to a man who has a phD in skin cancer and over 20 years of clinical experience, it's wise to avoid.

8. Yes, you can find a sunscreen that doesn't give you spots

Dermatologist Stephanie Williams feels your pain when it comes to SPF-induced breakouts. "It's not really the UV filter itself that causes spots, its more how the cream is formulated around the filter. Avoid creams that have a greasy texture and don't sink into your skin after a couple of minutes. A good starting point is any sunscreen that states 'oil free' on the bottle." So we guess using the same sunscreen for your body, as your face is a no, no? "I haven't found any body sunscreens that I would recommend to my patients on their face". Two sunscreens it is then.

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