I wanted so desperately for this product to work for my PIH/acne scarring. I just did not get the same results that everyone who praises this product got. I tried applying in the morning with sunscreen, in the nighttime, or both 2x a day. I initially applied this product without a pH balancing toner; I thought that might have been the problem, so I bought Mizon's AHA & BHA Daily Clean Toner (well-recommended pH balancing toner) to use with the OST C20. No change in result. I also initially applied BHA and AHA after, respectively, but then I tried applying only the OST C20 without actives afterwards to see if that would make a difference. Note that I am coming to these conclusions after having gone through two bottles of the OST C20, so I tried each change in method for about 1-2 weeks.

I know the picture shows my bottle is crystallizing but the picture was taken after I essentially gave up on the product and stopped using it. I kept my bottles in the refrigerator all the time, so any ineffectiveness was not due to improper storage.

I think I might try the C21.5 in the future, but for now, I'm done with the C20.