Block visible light. Hiding the cast is the bonus.

The SPF number and the UVA rating cover ultraviolet, and tinted or not, the protection is the same. Neither says anything about visible light, the light you can see, and its blue end triggers pigmentation, October included. Iron oxides, the pigments that give a tinted sunscreen its colour, block it. Hiding the white cast is a nice side effect, not the job.

The evidence is small but clear: in a six-month trial of 40 women with melasma, pigment came back about five times as much on the untinted version of the same sunscreen. The catch is dose. You want around 3% iron oxides and almost no brand prints the number, so the rule of thumb is that if you can't see the tint on your skin, it isn't blocking visible light. On the label, look for CI 77491, CI 77492 and CI 77499 near the top.