What exactly is an SPF?

Living in Australia means most of us grow up in the sun and from an early age we’re educated on how to be sun safe. From the good old Slip, Slop, Slap message right through to the consequences of too much sun exposure and the signs of sun damage to look out for – we’d consider ourselves a pretty educated bunch.

What exactly is an SPF?

But when it comes to sunscreen and an SPF rating, how educated are we really? In many cases, we look at the numbers and automatically assume that ‘bigger is better,’ but it’s a little more complex than that.


What exactly is an SPF?

The Sun Protection Factor (SPF) measures the protection a sunscreen provides from UVB rays, the kind that cause sunburn and contribute to skin cancer. This rating does not however measure how well the sunscreen will protect from UVA rays, which are also dangerous and damaging.

The SPF number tells you how long it would take for your skin to redden from the sun’s UVB rays i.e. SPF 15 would be 15 times longer, SPF 30 would be 30 times longer etc.


Other factors that affect your protection factor:

But as the name suggests, an SPF is a measure of protection and not a measure to help you determine how long you can spend in the sun. 

There are a number of other factors that also affect your level of protection, including:

  • Your skin type
  • Your location and the time of year
  • The weather conditions and the intensity of sunlight
  • How much you sweat
  • How long you swim and how well you dry off afterwards

Another major factor is how much sunscreen you apply. SPFs are determined by tests in which a liberal amount of sunscreen is applied, and many of us don’t actually apply enough sunscreen to achieve the listed SPF.


So is bigger, better?

Although the differences in SPF values seem to be quite large, there is actually little difference in how much UVB they filter.

An SPF 15 will filter out approximately 93% of the UVB rays, while an SPF 30 will filter approximately 97% and an SPF 50 will filter approximately 98% of UVB rays.


While SPF values are of course important, the best thing you can do to protect yourself is to make sure you are applying your sunscreen properly and regularly and of course being sun smart. You should also look for a sunscreen that is broad spectrum and provides protection against UVB and UVA rays.


Jo x


P.S. Typically physical sunscreens (like our Sun Juice) provide a natural broad spectrum solution for sun protection. You can read more about these here.

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