A keloid is a scar that will grow bigger and wider than initial injury when scar tissue grows excessively. They are usually firm, smooth, and hard growths due the spontaneous formation of scar formation. Places they are typically found on the body are the shoulder, breastbone, upper chest, and back, earlobes, and face. They are most common in the breastbone and shoulder area, but can occur anywhere on the body. Sun exposure can cause them to become darker; therefore avoiding sun for these areas is usually encouraged. 

They arise soon after injury, or can even develop months later. Typical injuries this can occur after are surgical incision sites, acne scars, ear piercings, burns, vaccination sites, scratches, and chicken pox scars. The precise reason that wound healing sometimes leads to keloid formation is under investigation but is not yet clear. 

Most people never develop this kind of scarring. However, others are more prone to them. According to the American Osteopathic College of Dermatology (AOCD), an estimated 10 percent of people experience keloid scarring. Those who are prone to them can develop keloid scars after minor injuries such as acne spots or bug bites. Those with a darker complexion are more likely to develop a keloid scar. If you are pregnant, and under 30 the likelihood of you developing one also increases. Those with a genetic component, meaning their parents or someone in their family experienced keloids, are more likely to develop them. Men and women are equally like to develop them. 

Keloids are not dangerous. People tend to seek treatment for cosmetic reasons specifically. Some experience pain or irritation with these scars, but they do not change into skin cancer. The problem with developing these scars is often times it grows back after treatment, demonstrating why this type of scarring is so frustrating for patients.