A keloid scar forms from abnormal healing, and usually develops in people 10 to 20 years old.
A keloid, or keloid scar, is a kind of overgrown scar, or an overly aggressive healing response to a wound.
It's a type of thick, irregular scar that rises above the skin level and extends beyond the original wound boundaries.
Keloids most often develop in people who are between 10 and 20 years old, according to the National Institutes of Health (NIH).
They're also more commonly found in people of African American, Asian, or Hispanic descent.
What's more, some people may be genetically predisposed to getting keloids, considering that more than 50 percent of people who get keloids have family members who also have the scars, according to a 2011 report in the journal Molecular Medicine.
Excessive scarring was first described in an Egyptian papyrus that dates back to 1700 BC.
It wasn't until the 1960s and 1970s, however, that modern physicians differentiated excessive scars into two types: hypertrophic and keloid scars.
Both types of scars rise above the skin level, but hypertrophic scars, unlike keloids, don't extend beyond the original wound.
Numerous other differences between the two types also exist.
Hypertrophic scars start to develop within two months of a traumatic injury, rapidly grow for up to 6 months, and then slowly regress over a few years until they stabilize.
They also tend to develop in body areas with high tension, including the shoulders, neck, knees, and ankles.
Keloids take several years to develop after a minor injury, sometimes form spontaneously in the mid-chest without a preceding injury, last for many years, and don't spontaneously regress.
They tend to form on the chest, shoulders, earlobes, upper arms, and cheeks.
Additionally, keloids often recur after being surgically removed, which rarely happens with hypertrophic scars.
During part of the normal wound-healing process, fibroblasts — a type of cell in connective tissue — synthesize the protein collagen, which provides structural support for the wound and plays a key role in each phase of wound healing.
Keloids form when the fibroblasts produce far more collagen than what's produced during normal wound healing.
In fact, the collagen synthesis in keloids is about 20 times greater than in normal, unscarred skin (and three times greater than in hypertrophic scars), according to a 2009 report in the journal Dermatologic Surgery.
Other biological factors also contribute to keloid development, including the overproduction of certain growth factors and glue-like proteins.
Keloids can develop from most types of skin injuries, including:
Keloids form over the general site of the
If exposed to the sun during the first year of formation, a keloid may tan darker than the surrounding skin — sometimes permanently.
For some people, keloids are more than just unsightly skin imperfections.
The scars can dramatically affect people physically and psychologically by causing tenderness, itchiness, and pain.
And these symptoms may worsen if the keloid is irritated by friction against clothing or other materials.
Aside from surgery, other options to reduce the size of a keloid include:
Scientists are currently investigating numerous other promising therapies for keloids, including: