This short post is meant to help you understand which SPF rating might be right for you to use.
I wrote a post explaining what SPF is but for now, this should address a lot of the questions we've been getting.
Read more: What is SPF?
I never like to assume people read all my posts (kind of understandable) so let’s start with first principles.
The basic facts
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.
Because UVA, UVB and UVC wavelengths are shorter than visible light, they are invisible to the naked eye. UVC doesn't make it to earth so we only need to be concerned by UVA and UVB, both of which are known to damage the skin, cause ageing and cancer.
What this all means for you and your sunscreen?
SPF is a measure of how much protection a sunscreen can give you against UVB only.
There are separate measures for UVA and you should always choose a sunscreen that protects against both UVA and UVB.
Back to the UVB…
The higher the SPF rating, the more UVB a sunscreen can absorb or ‘filter’. However, it is not linear So, for example, SPF 50 is not 2x stronger than SPF 25.
This is best shown as a chart.
As you can see, there is only a very slight difference between SPF 30 and SPF 50.
SPF 30 absorbs 97% of UVB and SPF 50 absorbs 98% of UVB. No sunscreen is able to filter or 'block' 100%.
UVB is the main cause of sun burn and plays a key role in skin cancer. The more UVB you can block the better. On average, your risk of melanoma doubles if you have had more than five sunburns in your lifetime.
Seeing this chart might explain why I always recommend SPF 30 as a minimum, wherever you are, whatever time of the year.
If you are particularly close to the sun geographically (e.g. in the tropics) or spatially (e.g. up a mountain) SPF 50 is imperative. SPF 50 is also imperative for babies, children and fair-skinned people. As the chart shows, for the sake of a few percentage points, you may as well go high. That's what I now do.
I know that most people judge SPF based on how much they do or don’t want to get tanned on holiday. But a tan is the body’s defence mechanism. A tan is the skin telling you it’s in trouble. A tan is damage. And damaged skin can lead to all sorts of bigger problems.
A higher SPF rating not only blocks more UVB but it protects you for longer (assuming the sunscreen isn’t wiped off somehow). It’s so simple: if in doubt, go high.
And if you do want a tan, fake it. But when in the sun, please protect yourself. Use a really good sunscreen. Wear a hat. Wear sunglasses. Cover up with clothing. It’s boring but it could save your life.
That’s it for now. Rant over.