I have lots of info about acne in my notepad, click the link in my signature .... there's a lot you can do to improve acne besides just switching mu (though that can help a lot!)
You'll have the best luck if you buy a foundation (and concealor and powder, if you use them) that is labeled non-comedogenic or non-acnegenic because they will be least likely to clog your pores. Products labeled only oil-free will not have oils but may have other greasy pore-clogging ingredients. However you may still have to try several products to find what works best for your skin -- the FDA has no official definition for non-comedogenic/non-acnegenic so *technically* a company can give any product those labels. Plus what clogs one person's pores may not necessarily affect another person.
I've never tried powder foundations, but I do know that loose powders are better than pressed powders for oily or acne-prone skin. My dermatologist told me to never use pressed powers, because pressed powders contain oils to press them into the compact. In fact, my dermatologist told me to only wear Prescriptives brand foundation, concealor, and powder since he insisted that was the only brand that was truly non-comedogenic. However lately I've been wearing drugstore mu that seems to work just as well for my skin. (L'Oreal Mattique Foundation, CoverGirl Professional Loose Powder - awesome for preventing shine, and several concealors that I haven't been happy with
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Hope that helps!
