Use exactly a pea sized amount. Less is more with this product, as using too much will probably cause you irritation and redness.
If you have sensitive skin, I would suggest only using it twice a week and see how your skin reacts. If your skin responds alright, use it three times a week, then four, etc. etc. If, however, after using it twice a week and your skin looks tender, red, or peely, just keep using it twice a week until your skin gets used to it.
Good luck! Hope it helps you