I've been using this serum twice a day for about a week now and I love it! When I first began using it, it did cause a slight tingling sensation but after reading up on vitamin C, apparently that's pretty normal as your skin adjusts to it. If you have sensitive skin, you'd probably want to start with a small amount. By the third day, I didn't feel a thing. In terms of its efficacy, it did a really good job at helping to fades dark spots. It's also left my skin feeling smoother and brighter.
