Are the labels on your sunscreen really accurate?
This is small study conducted by a Japanese company (they sell spectrophotometers etc) on 6 different (prob Japanese) sunscreens by applying 2mg/2uL per cm2 on human skin (living volunteers, not ex vivo expts) in 2015. I'm not going to translate everything but scroll to the last page and look at the results table.
On the left of the table shows the 6 diff samples and their SPF and PA labels.
On the right of the table shows the actual SPF and PA measures according to their measurement.
Basically, all sunscreens did not hit the mark (as indicated on their labels, esp UVA protection) except for Company A sunscreen 3 (although I'm a bit iffy about the ridiculously high SPF and PA measurement values).
Still, food for thought. Apply more sunscreen, and apply more often. Labels are not accurate I guess.