Some scars grow lumpy and larger than the wound they are healing. This is called keloid scarring. It can happen to anybody, but is more common in people with dark skin, such as people from African, African-Caribbean and south Indian communities.
The body's tissue naturally heals itself when it is damaged. This healing process can cause scars to appear.
If the skin is broken (for example, by a cut, bite, scratch, burn, acne or piercing), the body produces more of a protein called collagen.
What are keloid scars?
Collagen gathers around the damage and builds up to help the wound seal over. The resulting scar usually fades over time, becoming smoother and less noticeable.
However, some scars don't stop growing. They "invade" the surrounding healthy skin and become bigger than the original wound. These are known as keloid scars.
Some scars become red and raised within the size of the original wound. These are called hypertrophic scars. Find out more about hypertrophic scars.
"A keloid scar is an overgrown scar that can spread outside the original area of skin damage," says Hermione Lawson of the British Skin Foundation. "Keloid scars are shiny and hairless, they're raised above the surrounding skin, and can feel hard and rubbery."
Keloids affect around 10-15% of all wounds. They can appear anywhere on the body, but usually form on the shoulders, head and neck.
They can last for years and sometimes don't form until months or years after the initial injury. New keloid scars are sometimes red or purple. They're not usually painful, but some people feel embarrassed or upset if they think the scar is disfiguring them.
Experts don't fully understand why keloid scarring happens, but these scars are not contagious (they're not catching) and there is no risk of them turning into cancer.
Who gets keloid scars?
Keloid scars can affect anyone, but some people are more likely than others to get them. "People with dark skin get keloids much more easily than people with fairer skin, and it's common in people with black skin," says Lawson. It's thought that keloid scarring may run in families.
Keloid scars can develop after even a very minor injury. "Burns, acne scars and wounds that get infected are particularly likely to form keloids," says Lawson.
"You're at higher risk of getting a keloid scar if you have had one before."
Can I reduce the risk?
You can't stop a keloid happening, but you can avoid any deliberate cuts or breaks in the skin, such as tattoos or piercings, including on the ear lobes.
What is the treatment for keloid scars?
There are several treatments available, but none have been shown to be more effective than others. Treatment can be difficult and isn't always successful. Treatments that may help flatten a keloid include:
- steroid injections
- applying steroid-impregnated tape to the area for 12 hours a day
- applying silicone gel sheeting to the area for several months, although a review of studies found that it is unclear whether this works or not to prevent or treat keloid scars
Other options are:
- freezing early keloids with liquid nitrogen to stop them from growing
- laser treatment to lessen redness (this won't make the scar any smaller)
- surgery to remove the keloid (however, the keloid can grow back and may be larger than before)
If you're bothered by a keloid scar and want help, see your GP.