And put it on properly. This means reading the instructions.
They do not say - slap on head just before sprinting out the door and getting a sweat on.
Ideally a shower to remove grease, then put on P20, then wait for it to dry, then a second layer, and wait for it to dry, then possibly a third to be sure. Seems excessive but depends on if you are doing an all day event and want to avoid burning or just nipping out for a 5k lunchtime run.
M.eface