Not very clear, but petrolatum aka petroleum jelly is used as a barrier so stuff doesn't get into the wound when the skin is compromised. This helps with anti-microbial defense and wound repair.

https://www.jacionline.org/article/S0091-6749(15)01194-X/fulltext

Petrolatum is a compound found in sunscreen.

He started working outdoors AKA getting sunburns (if left unprotected, lower lips are one of the prime locations where people can develop squamous cell cancer later on). He should really use sunscreen, which is a barrier (absorbs the UV rays so the skin does not-- rather than deflecting the sun rays.)