I bought this serum to introduce myself to the vitamin C world. However, I am not sure if this serum is doing anything for my skin in terms of vitamin C. I have been using it continuously for the last 3 months and I think I see a bit brightening on my face and neck which I suspect comes from 20% niacinamide that is present in this serum. I will not repurchase this since I am planning to go into more stronger vitamin C serums. Lastly, it did not irritate my skin in any way. I use it when my skin barrier is damaged and it does not sting. I also use it on damp or wet skin and no irritation occurs.