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What is SPF?

Updated: Dec 16, 2020

SPF stands for sun-protection factor.

It's important to understand what SPF means, and which SPF products to use.

The risk of skin cancer is much greater when the skin is exposed to the sun for longer periods of time.

How is SPF measured?

The SPF factor is measured by how much sun exposure your skin could tolerate before burning, compared to how long it takes for your skin to burn with an SPF applied.

If you would naturally burn in the sun after 10 minutes, and you applied an SPF factor of 30, your skin would stay protected for 10 x 30 minutes. So, you would be protected for 300 minutes (5 hours).

But this isn't strictly true...

You cannot apply a moisturiser with factor 60 and say that you're set for the day - or say you don't burn in an hour in the sun - so a low factor will suffice.

What does an SPF do?

SPF prevents photons from hitting your skin.

Photons are both particles and waves, they are highly charged and can cause chemical changes to the skin cells they interact with. The photons have enough energy to interact with the cell's DNA. If the DNA in those cells becomes too damaged, the cell dies - in other words, burns.

Sun protection factor products prevent this from happening by not allowing the photons to reach the skin as much - but it's still doesn't stop 100% of the photons.

If you are wondering how sunscreens prevent photons from penetrating through to the skin, you can read all about it here.

Do all SPF products protect from photons the same?

No, different SPF values protect the skin at different efficiencies. The higher the SPF value, the less photons that hit the skin.

No sunscreen

If you expose your skin to direct sunlight with no SPF factor you will get 0% protection - which means all 100 photons will hit your skin.

SPF 15

If you use an SPF of 15, you will get 93% protection - leaving only 7 photons to hit your skin.

SPF 30

Using an SPF of 30, it will provide 97% protection - leaving 3 photons to hit your skin.

As you can see, the relationship between SPF value and protection is not linear. This means, that the higher the SPF we use, the less photons will come in contact with our skin.

SPF advice

Protecting your skin from photons is extremely important at any age.


You should be applying an SPF product which protects from UVA rays on your face daily.

There are many products available on the market, from moisturisers to bb creams.

Personally I used a physical sunscreen on my face with an SPF of 20.

If you would like to learn more about the differences between physical and chemical sunscreens, click here.

During the summer:

As the sun becomes more direct, and the days get longer - it's important to take extra care against photons.

The lighter your skin tone, the higher the higher the SPF you should be using, due to the lack of melanin in your skin.

You should be applying at least 2mg/cm2 of skin - which is much more than what you're like used to.

You should also re-apply your sunscreen every 2 hours, despite of the SPF value.

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