Keloids are the excess growth of scar tissue at the site of a healed skin injury.
Keloids usually are not medically dangerous, but they may affect appearance. In some cases, they may become smaller, flatter, and less noticeable over a period of several years. (Source: http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001852/)
Hypertrophic scars are excess deposits of collagen that can form after a skin injury.
While both of these types of scarring can happen as a result of a body piercing, the bumps that sometimes appear on a piercing are often misidentified as a keloid or hypertrophic scar, when more often than not they are symptoms of irritation due to things such as improper aftercare, poor quality jewelry, physical irritation/pressure, or incorrect placement of the piercing.
Though hypertrophic scars and keloids are a possibility, diagnosing a bump as either is best left to a properly trained medical professional.
Cody Vaughn - Outreach Committee