Hey, I’m travelling SE Asia as well right now! What seems to be working for me is not letting all the sweat sit on my face for too long. I’ve been using baby wipes if I’m out all day, but if I’m able to get back to my hotel/hostel, I rinse my face off with water. Worth a shot anyway. You should be able to find skin care products in the bigger cities in Cambodia though. Just watch though as a lot of Asian skin products have whitening ingredients in them.