What the SPF? Sun Protection Factor explained.

Skin cancer

Posted on 08/04/20

I’m often amazed at how misunderstood the term sun protection factor (SPF) is in the context of sun care. Particularly considering it is such an important factor (excuse the pun!) in what you choose to buy when hitting the sunscreen fixture in a store. 

I sometimes think it’s like when a child asks you how Bluetooth works and you feel unbelievably stupid because the best explanation you can offer is that “stuff goes through the air”.

So, I’m going to demystify SPF in ten (hopefully) simple points. Because simple works best for me.

Point #1

Rays from the sun reach the earth. Some we can see. Some we can’t. The rays we can’t see are called ultraviolet light. Ultraviolet light or ‘radiation’ comes in different wavelengths: UVA, UVB and UVC. 

Point #2

UVC doesn’t make it to earth. UVB does a fair bit. UVA does a lot. Poor English, I know. It was intentional.   

Point #3

I repeat this a lot in this journal but here it goes again….

The World Health Organisation classifies ultraviolet rays as a probable human carcinogen.

To support that, a UK study found that 86% of melanoma cases are caused by ultraviolet light from the sun. 

Point #4

UVB causes sun burn. Think ‘B’ for burn

UVA can also cause sun burn but it penetrates deeper into the skin, damaging the natural proteins under the skin’s surface. These proteins keep the skin tight and strong. The proteins get damaged and the skin loses its strength and support. Like if you took the filling out of an apple pie, the pastry on top would cave in. That’s why the sun causes skin ageing. Because of UVA. Think ‘A’ for ageing.

Point #5

Both UVA and UVB cause or enhance the development of skin cancer.

See point #3.

I thought it was worth wasting a point to reiterate this one again.

Point #6

A good cream blocks both UVA and UVB. This is what broad spectrum means on some sun cream labels. Always buy broad spectrum or products that say they protect against UVA and UVB on the packaging.

Point #7

Getting to the nuts and bolts….SPF is the level of protection a sun cream gives against UVB ONLY

Observe the CAPS. That bit was key. 

Somewhat unhelpfully, UVA has an entirely separate measure.

Also read: Understand the risks of UVA. Your attitude to skincare will change forever

Point #8

Without any protection, the human skin will burn when exposed to UV. We’ve all been caught off guard.

If you’re fair, this could be as little as 5 minutes. If you’re darker, it could be 15-20 minutes.

Point #9

If you have an SPF cream of 10 and your skin burns naturally (without protection) in, say, 10 minutes, the bottle of cream you are holding will protect you for 100 minutes before you need to reapply

i.e. (SPF 10) x (your natural burn limit of 10 minutes) = 100 minutes total protection time.

Where everybody goes wrong is dosage.

If you use too little of the cream, you’re effectively reducing the SPF on the left-hand side of the formula. SPF 10 could become SPF 5 because you used half the recommended amount. You got it. 100 minutes becomes 50 minutes. When people say, “I burnt even though I had cream on”, this is probably the reason.

Point #10

For those of you interested, this is how a European sunscreen product gets ‘awarded’ its SPF rating….

Firstly, the exercise is carried out according to an international standard and must be performed under dermatological control in an accredited laboratory.

The test itself uses a special lamp that effectively simulates the sun’s UV light. The lamp is pointed onto the skin of a test human with and without the sample sunscreen. The response of that area of skin to the lamp allows the lab to determine the protection provided. The way they judge if a product is working or not is if the skin shows signs of erythema – a fancy way of saying skin reddening or sun burn. One area of skin is exposed to the lamp without any protection and another is exposed with the sunscreen product in question. Finally, a third area is exposed using an SPF reference product for validation.

To determine the SPF, a series of delayed reddening responses are induced on several small sub-sites on the skin. These responses are visually assessed by a dermatologist for the presence of redness 16-24 hours after the UV radiation.

The result is an SPF score based on how the skin responded with the test sunscreen. This is called an in vivo test. Obviously, as LifeJacket skincare products are all clinically and dermatologically tested, our products have been scrutinised by these tests.

Conclusion

So that’s it. Hopefully clear. If not, please message me. Sorry for the maths and technical stuff at the end but a lot of you ask for it on our webchat so I felt it was worth sharing,

As I always say, avoid the risks and just wear sun protection all year round. Wherever you are and whatever the weather. Making it part of your daily regime is so simple and it will keep you looking younger and fresher for longer. 

Thanks so much for reading. 

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