There are 2 common bumps that occur with a piercings and they are; bacterial pocket and hypertrophic scarring (granulation tissue). These occur when the piercing is traumatized. In the case of a boil (bacterial pocket) a small tear allows microbes to enter the piercing. Boils are often painful and red, and may secrete pus or blood. The other most common bump is a hypotrophic scar. Nose and cartilage piercings, especially industrials, are prone to this type of scar. This type of bump surrounds the exit hole, It is often the same color or a bit darker than your skin and It may feel hard, but often are not painful. They are usually caused by the mere presence of the jewelry and the body's response to protect itself.