To get the Skin Care achievement, you must have both Oily Skin and Rotted Breath on you. Slay the piper when it spawns at 70% then stand behind Zlandicar and wait. Eventually he will hit your groupmates with both Rotted Breath and Oily Skin. Even though the buffs may be refreshed, having them on you for about 5 Mins each will net you the achievement. Its a personal achievement, so each toon that wants the achievement, must land both debuffs on them for around 5 mins duration.
Hope this helps