All of us have heard of Sun Protection Factor (SPF). This official measurement was sanctioned thirty years ago by the Food and Drug Administration (FDA) in the USA.

Multiply the SPF number by the burn time of the day to calculate the duration of your protection. Burn time is losing popularity as a term, but it is still the easiest way to work it out.

As the diagram shows, if your burn time is 20 minutes, then an SPF 12 lotion should protect you for 12 x 20 minutes. i.e. 4 hours.

To get pedantic, if you cover yourself with SPF 12 lotion, and sit in the sun between 10am and 2pm, you will get sunburnt.

What’s missing with SPF? SPF only measures UVB protection. SPF does not measure UVA protection.

That’s right. It will not tell you the extent of your lotions protection from UVB, DNA damaging, age causing rays. Unlike UPF which measures the entire UV spectrum.

Many sunscreens claim to have broad spectrum coverage. By this they are claiming to also sheild against UVA rays, as the diagram shows. However, they cannot state which part of the UVA range they protect from, nor the degree of protection.