You can basically treat it like you would a sore on you. Clean it and maybe use some peroxide and then neosporin. Vaseline will help keep bugs out of it, if that is a problem.

It only takes one fly to slip into your house from outside and then start reproducing. They eat garbage and food so they just keep multiplying if you do nothing. The clear sticky fly strips you put in the doorway have worked the best for me short of bug bombing a house.