What Does SPF Mean, and Why Is It the Only Anti Ageing Step Everyone Agrees On?
Sun protection factor: how much longer skin takes to redden with the product on. Broad spectrum means it covers UVA as well as UVB.
On the label
SPF 30 or 50, broad spectrum, and in New Zealand the AS/NZS standard mark matters more than the brand.
What it does not mean
It does not mean once a day. Reapply if you are outside, and put it on after every morning serum.