The Burn Book: Why SPF is *so* fetch

A derm answered all your burning SPF questions, so you don't actually get ~ burned~
The Burn Book: Why SPF is *so* fetch
CosmoBy Cosmo -

IDK who needs to hear this, but I'm gunna say it again for the 100th million time: you need to be wearing sunscreen every day. I know, I know, the sun is great and all, but remember wrinkles? Sun damage? Cancer? Protection from UV rays is the most important thing you can do for your skin, so we spoke to Lisa Williams, education manager at Dermalogica to get the low-down on everything you need to know about summer’s must-have beauty product. Ready for a PhD in SPF? Okay, leggo…


Sun protection factor is a measure of how long a sunscreen will protect you from ultra violet rays.  The higher the SPF, the less UV passes through. So, for example, SPF 30 allows one thirtieth (or 3.3%) of UV to reach your skin. Look for sunscreens labelled ‘broad spectrum’, like Dermalogica, which have been FDA-approved and indicate that they have been tested and ensure adequate protection from UVA as well as from UVB.


UV radiation is a form of electromagnetic energy.  It can come from natural sources such as sunlight as well, as well as artificial sources, such as lasers, black lights and tanning beds.

UVA = Longest wave length
UVB = Medium wavelength
UVC = Shortest wave length

UVA rays penetrate deep into the skin and play the greatest role in premature skin aging. They are accountable for wrinkle formation and steadily destroy key substances in the skin that give it its firmness, like collagen and elastin. They are present all day long, 365 days a year – yes, even when it is cloudy and the sun isn’t out. 

UVB rays affect the skin’s top layer and are the primary cause of skin cancer, sunburns and discolouration. They harm the outermost layers of the skin and directly damage the DNA.  Although UVB does not penetrate as deep as UVA rays, it is still powerful. What’s important to know is that UVA can penetrate glass, while UVB rays do not. So even if you think you’re not going outside, if you’re sitting by a window or travelling in the car, your skin is being exposed to UVA rays, making sunscreen a necessity.

UVC rays are the shortest of all UV rays, they never reach the earth because the ozone layer absorbs it. These rays are usually not considered a risk for skin cancer and are found in manmade sources like mercury lamps, welding torches and school tanning beds.


Sunscreen should be applied every day. The best practice is to apply a minimum of SPF 30 in the morning, ideally 30 minutes before being exposed to the sun, and you should reapply every two hours.

Ideal dosage

1 teaspoon for the face and neck. 7 teaspoons or 35ml of sunscreen for one full body application.

Add it to your skincare routine

This should be the last step in your skincare routine, so you should apply this after your serum and moisturiser. 


Sensitive, dry and acne-prone skin

Physical sunscreens work by creating a barrier on the skin that filters out UV rays - these are sometimes called sun blocks. They use mineral-based ingredients, like titanium dioxide and zinc oxide, to stay on the top of the skin and block, deflect and scatter damaging UV rays away from the skin. Annoyingly, they can rub and rise off easily, and as they are quite thick in viscosity, they can sometimes look chalky, feel heavy under make-up, and even increase sweating. Sensitive, dry and acne-prone skins will benefit as there is less chance for any potential irritation.

Dermalogica Invisible Physical Defence SPF 30, Dhs282 at

Dermalogica Super Sensitive Shield SPF 30, Dhs265 at

La Mer The Broad Spectrum SPF50 UV Protecting Fluid, Dhs457 at Bloomingdales

Kiehl's Ultra Light Daily UV Defense Mineral Sunscreen, Dhs210

Ageing, oily and hyper pigmented skin

Chemical sunscreens contain chemical compounds like octinoxate, octisalate and avobenzone, which absorb UV rays. These chemicals change UV rays into heat, which is then released from the skin and scattered, and are great for people with darker complexions, as they easily absorb into the skin and feel much lighter compared to physical sunscreens. They are also a great option for people with more challenging skin concerns, like ageing, oily prone and hyper pigmentation.

Dermalogica Dynamic skin recovery SPF50, Dhs351 at

Dermalogica  Prisma protect SPF30, Dhs228 at

Clarins UV PLUS ANTI-POLLUTION SPF 50, Dhs232 at Bloomingdales

Shiseido Urban Environment UV Protection Cream Plus SPF50, Dhs220 at Sephora


Unsurprisingly, there are a whole bunch of myths around sunscreen that you need to stop believing. Lisa Williams breaks down the three most common…

“The higher the SPF the more time you can spend in the sun.” 

This is a common misconception. The only thing that high SPFs contain is a false sense of security.

“Wearing make-up with SPF is enough.”

Foundation or other beauty products containing SPF often only protect against UVB rays, meaning you’re not protected through car windows, office or home windows and cloudy weather.

“You don’t need to wear SPF indoors”

Whether it’s Zoom meetings or virtual workouts, our screen time has shot up recently, which means we need to protect our skin from blue light, the harmful energy produced from our digital screens, like TVs, smart phones, computers, laptops, and fluorescent lighting.