I found out that dermatologists don't know much about acne because they are trained in skin diseases, and skin care is different than skin medication.
I had a friend whose acne was -caused- by the cearasil she was using, becaue the high alchohol levels were irritating her skin.
And I, personally, am allergic to dyes and fragrances, so I have to use dye and fragrance free skin products or I break out.
Different things work for different people.
Here in an in-depth coverage of what causes blemishes and how to deal with them:
Zit info