Since this is a popular serum, I found a mini size and decided to give it a try. After purchasing, I realized that it's actually an introductory serum (booster)... I bought it thinking it was a serum to be used after applying lotion. The tingling sensation caused by the needles was as expected. I guess it takes some getting used to, but after using it 2-3 times, it didn't feel comfortable... For some reason, even after applying it the morning after, after washing my face and then applying other skincare products, I still felt a tingling sensation in some areas, which I felt was irritating, but is this supposed to last for such a long time? I'll try using it a few times to see how it affects my skin. If it works for my skin and I get used to the irritation, maybe I'll buy it again?