There are numerous websites that recommend penis exercises to increase the length or girth of the penis. The rationale behind these exercises is that repetitively rubbing the penis creates "micro-tears" in tissues that look engorged when healed. There is one popular technique called jelqing in which the thumb and forefinger are wrapped around the penis to repetitively stretch the shaft from the base to the tip for 20 minutes every day. Despite claims to the contrary, there has never been any evidence that physical exercise of any sort, including jelqing, can increase penis size. In fact, the persistent rough handling of the penis can cause injury or scarring.