I have adult onset hormonal acne (with PCOS) and it's very difficult to treat. For me, when acne is crazy out of control, hugely swollen and red, really painful and deep under the skin, this stuff helps me get through it. It helps severe breakouts resolve faster. It soothes the big painful blemishes, quickly reduces redness and swelling, dries pimples out, and makes blemishes come to the surface faster and heal faster.
I don't think it does much to prevent acne and I wouldn't recommend it for daily use, but I use it whenever I am really fed up with my skin and it always noticeably improves my skin overnight. It isn't going to make your skin perfect all the time, but it helps when you are having a bad time. It's the best thing I've found to use for a spot treatment.
When this stuff dries on your face, it's so absorbent it sucks a lot of crap right out of your face. It does pull a lot of the oils out of your skin so if your skin tends to get dry just be careful. You might not want to use it too often or leave it on too long, or you may just need to use plenty of moisturizer when you remove the mask.
I see a lot of people on here complaining about the smell and I honestly have never thought that it smelled bad. I think it smells like clay or chalk. I think it's a clean soothing smell, not gross at all! It does contain sulfur so maybe some people are more sensitive to the smell of sulfur than I am?
I've tried a lot of proactiv products and this mask is the only one that ever really gave me any results.