sentences:  This became a significant problem for dermatologists in the 1970s and 1980s, but with the improved formulations produced by cosmetic chemists , a diagnosis of acne cosmetica has become relatively rare daily dermatological practice.The terms "non-comedogenic" and "non-acne(i)genic" appeared on moisturizers and other cosmetic compounds as manufacturers introduced re-formulations—sometimes associated with claims that the products were "oil-free" or "water-based".Although early work produced lists of comedogenic chemicals in various strengths and vehicles, it became apparent that one could not predict the actual comedogenicity of a product from its contents; rather, the finished product itself needed use-testing.