Sometimes I'd pick too far into my skin, and my finger would begin to sting, like a paper cut. So, I'd move on to another finger. Eventually it got to a point that I was damaging the skin to the extent of bleeding. And I didn't know it at the time, but I was opening up my fingers to all kinds of bacteria. "You can create an open wound and increase your risk of infections," says Joshua Zeichner, MD , director of cosmetic and clinical research at Mount Sinai Hospital. "Bacterial infections are most common, and they can lead to what is called an acute paronychia, where bacteria enters the skin [around the nail] causing a red, painful finger that may fill up with pus." Thankfully, it never got that bad for me.