Probably a bit late to "stop it" now, since it is already rusted and chipped. What causes it is the molding rubber strip that rubs it (between the bumper and the headlight facia). A known issue. That rubber strip rubs against there and holds moisture and causes this.
Before mine started doing it, I raised up the rubber strip and put a piece of matt black vinyl wrap...So the rubber is not against the paint any longer.
Given how far along your looks now, you might need to get that resprayed. Then put clear or other vinyl wrap (or take the rubber strip off).
Good luck.
DC