It's effective when your skin feels a little dry. When I used it in the summer, I didn't see the benefits and stopped using it. When I tried it again in the winter, I noticed an improvement in the stinging sensation caused by dryness. It leaves a slight film when applied, so I wonder if that helps prevent dryness? In my case, I used to put it away because I felt like using too much during humid seasons could lead to breakouts, but in the winter I can use it almost every day without any problems. I use about half a dropper, depending on how dry my skin is. This is just my personal opinion, but if you buy from CNP Laboratory, the dropper-type series is more effective than the spray-type, so if you're interested, try it here!