If you tend to put on an old factor without paying much attention to how much protection you need, or swear you’re a factor 15 person but find yourself eventually sunburnt, a simple bit of sunscreen can help. mathematics are needed.
It’s tempting to assume that your personal SPF is a simple calculation of the time it takes you to burn multiplied by whatever the factor is. So if you burn after 10 minutes in the sun, using a sunscreen with SPF15 should mean you can safely stay in the sun for 150 minutes before you burn. But for most people, that won’t be the case.
The British Association of Dermatologists says a safer way to think about it is that applying an SPF15 sunscreen results in UV exposure “one-fifteenth of what you would have gotten if you hadn’t applied sunscreen.”
Animal, vegetable or mineral – how “natural” should your sunscreen be?
Sunscreens are often split into two camps, labeled “mineral” or “chemical” on the packaging. The names are somewhat misleading, says Prof. Diffey, because all sunscreens contain chemicals in one way or another. Specifically, sunscreens contain organic or inorganic UV filters, or, as with most standard sunscreens, a mixture of both.
“What manufacturers often do today is take two or three organic chemicals and mix that with a non-organic chemical like titanium dioxide,” says Prof. Diffey.
Inorganic filters such as titanium dioxide and zinc oxide are often referred to as “physical” or “mineral” because they “reflect and scatter UV rays,” says Dr. Fassihi. They are most commonly found in children’s sunscreen and can leave a white residue on the skin and feel a little greasy.
“Sunscreen chemical ingredients are effective at absorbing UVR and are much more cosmetically acceptable,” says Dr. Fassihi. They tend to have a lighter feel, which means they go on more easily.
For Dr Sarah Tonks, a dermatologist at the Lovely Clinic in London, chemical sunscreens are a no-go. “I don’t use chemical sunscreens. First, it gives me acne, and second, I’m worried about the [impact on the] coral.”
National Geographic estimates that 14,000 tons of sunscreen wash into our oceans each year, which can be toxic to marine life and coral reefs. Holland & Barrett banned chemical sunscreens earlier this year. Meanwhile, dermatologists say “mineral” sunscreens irritate your skin less.
Ultimately, they both protect the skin, so it’s best to find one that you really enjoy applying.
Once a day sunscreen doesn’t work
Which? tested once-daily sunscreens in 2016, and found a 74 percent reduction in protection at the end of a day of wear. Both Cancer Research UK and the British Association of Dermatologists advise against its use, and it’s worth noting that they are banned in Australia. They risk giving you a false sense of security when you could rub the cream off your clothes and noticed that protection wears off after swimming.