I was just reading about sebum on Wikipedia.  (Here’s a plug for learning about stuff online… Find it on Wikipedia and it will be pretty accurate.  You can go to the references section at the bottom of the screen for some links to more official sites and articles.  It’s a great way to learn about things.)  I read about how sebum is a natural skin lubricant made by your body.  Extreme skin treatments can cause it to be released in excess, which actually makes the skin more greasy that before. 

It defeats the purpose.  This is proof that in yet another context, it is never good to go to extremes.  If you use too much astringent on your face, you will dry the skin out so much that it will respond by releasing extra sebum.  It is better to stick with a daily consistent regiment of skin care, even if you occasionally have pimples.  Many skin care products are effective only if used as directed.  If you let it get out of hand and treat it too often, even the most mild cleansers and creams can have detrimental affects.  The practices that will pay off in the long run are the daily consistent habits of taking care of your skin.