if you're anal enough to do a "pre shampoo mask" i'm gonna go out on a short limb and assume you also use numerous other skincare products that claim to "treat" acne. All I can say is, don't, and stop.
A lot of people get on board the skincare/hairproducts train as teens because of natural teenage acne. And once you're on that train, if you ever stop using the acne-suppressing products, the acne comes back. But only at first! This is natural - when you're constantly de-oiling your skin, your body produces more oils to compensate. Then if you stop de-oiling, you of course get really oily - for a little while, a month or two. But in a pretty short time, your skin realizes it doesn't need to make so much oil, and slows down to a normal adult level.
I have the best skin & hair I've ever had since I stopped using anything but basic suave conditioner, and gentle soap only if I literally get dirty.
If you have never in your adult life held off from using products for at least two months, you actually don't even know what your natural adult skin & hair look like. There is an adjustment period but you have to resist the urge to treat issues with products.
Also if you eat more than 1-2 ounces per day of meat or cheese/butter you will get pimples and greasy skin because of it.