That can happen for various reasons, most of which are harmless causes like little tears (from straining) or a hemorrhoid. The blood that results when an older person has colon cancer doesn't look like bright red blood. It's darker and looks like coffee grounds. Bright red blood comes from lower down nearer the exit, which is why it doesn't have time to oxidize and turn dark. You're too young to have colon cancer, but you could have a little tear or fissue, some sort of ulceration, a hemorrhoid (which is basically a varicose vein there around the anus). If it continues, see your doctor. Also, watch what kind of toilet paper you're using and how hard you're wiping. That's a delicate area down there.