How SPF is tested
The laboratory method behind the number, the dose it assumes, and why real world protection is lower.
UVA, UVB and PA
Two parts of the spectrum, three rating systems, and how to compare a UK label with an imported one.
How much to apply
Six to seven teaspoons for a body, two fingers for a face, and what halving the dose really costs.
Does sunscreen expire
Period after opening symbols, heat damage, separation and when a half used bottle is no longer protecting you.
Reef safe claims
An unregulated phrase, a contested body of research, and a set of real destination restrictions.
Vitamin D
The trade off that mostly is not one, and why UK latitude matters more than your sunscreen.
Then apply it at the shelf
The eight category reviews turn all of this into a buying decision, scored out of 100.