In ancient times, when people died, their corpse is treated by chemicals and to be made as mummy. The chemical’s generative effect is to keep the corpse not to be rotten. The chemicals that prevent rotten in Korean language is “방부제” which is also used in preservative chemical to foods, skin cares, and so on.
In entertainment term, “방부제 미모” is often used to denote beauty which is retained when the entertainer is more than 50s of age, the witty sense of its meanings awe to the entertainer. The meaning of “방부제” is good sense, and feeling like jargon to the field.
Some people would perceive 방부제 as botox or so, it could make sense too, but generally the term is used to celebrate entertainer’s shiny face, removed its chemical’s negative meaning.
Examples:
“환갑에도 방부제 미모를 지닌 그녀는 여신이십니다” = “Although she’s 60 years old, she still has shines about her beauty, she is real goddess for the shines.”