What does the SPF number on a bottle of sunscreen really mean?

WE all know that the higher the sun protection factor of a sun lotion, the less likely we are to burn.

But what do the SPF numbers on bottles of sun lotion actually mean?

What do the SPF numbers mean?

If your skin always burns, even after you’ve lathered on the sun cream, there are various reasons why – but one common factor is the SPF you’re wearing being too low.

While some may think the ascending factors (10, 15, 20, 30, 50) are according to some random numerical scale, there is actually a significance to each grade.

Each number represents how many multiples of time you’re safe to be out in the sun before you start burning.

According to the : “If it takes 20 minutes for your unprotected skin to start turning red, using an SPF 15 sunscreen theoretically prevents reddening 15 times longer — about five hours.”

So, wearing a factor 15 sun cream will give you 15 times the number of minutes before you burn, than what you’d have with no sunscreen protection at all.

What is the UVA star system?

As well as SPF being listed on a bottle, you may notice there is a UVA star system on the side too.

UV radiation from the sun is emitted in three wavelengths – UVA, UVB and UVC – and we mainly need protection against the first two.

The UVA star system ranges from zero to five and indicates the ratio between the level of protection afforded by the UVA protection and the UVB protection.

A high level of stars indicates the ratio between the UVA and UVB protection is about the same.

A sunscreen with SPF 30 and four or five stars is generally  considered a good standard of protection, along with appropriate clothing and shade depending on the weather conditions.

Soaked up too many rays during the heatwave? Here’s how to get relief fast.

We revealed how to tell if your sun cream is out of date – and where to buy bottles from just £1.

We also highlighted the one part of the body you should always apply sun cream to… but probably don’t.