Keloids form when your body overreacts to a skin injury, producing far more scar tissue than necessary. Almost any break in the skin can trigger one: a piercing, a surgical cut, a burn, acne, even a minor scratch or bug bite. The key factor isn’t the severity of the injury but how your body’s healing process responds to it.
What Happens Inside the Skin
Normal wound healing involves your body laying down collagen, the structural protein that knits skin back together. Once the wound closes, collagen production slows and stops. In keloid formation, this process never shuts off. Specialized cells called fibroblasts keep producing collagen at abnormally high rates, along with excess amounts of other structural proteins like elastin and fibronectin. The result is a firm, raised mass of scar tissue that grows well beyond the edges of the original wound.
The collagen itself is different in keloids. Normal scars contain a balanced mix of two collagen types, but keloid tissue is loaded with an elevated ratio of type I collagen, which is thicker and more rigid. This is why keloids feel dense and rubbery compared to ordinary scars. The fibroblasts driving this process also behave unusually: they need fewer growth signals to keep multiplying, they respond abnormally to the body’s regulatory signals, and they produce elevated levels of inflammatory compounds that keep the scarring cycle going.
The skin’s outer layer plays a role too. After an injury, surface skin cells release a cascade of signaling molecules that communicate with the deeper tissue. In keloid-prone skin, this cross-talk between the outer and inner layers of skin appears to malfunction, pushing fibroblasts into overdrive instead of guiding them toward normal repair.
Injuries That Trigger Keloids
The list of potential triggers is surprisingly broad. Common ones include:
- Piercings and tattoos, especially ear piercings
- Surgical incisions, including C-sections and open heart surgery
- Acne, particularly deep or cystic breakouts
- Burns and cuts
- Shaving nicks and ingrown hairs
- Chickenpox, bug bites, and injection sites
What makes keloids unpredictable is that a person might heal normally from one injury and develop a keloid from another. The trigger doesn’t need to be dramatic. Some people develop keloids from injuries so minor they don’t remember getting them.
Who Is Most at Risk
Keloid risk is strongly tied to genetics and ethnicity. Prevalence varies enormously across populations. Studies have found self-reported keloid rates of 16% in Zaire, 9% in Zambia, and 11% in Ghana, compared to roughly 2% in Canada and 0.09% in England’s general population. In the United States, Black individuals between the ages of 10 and 30 carry the greatest risk.
Age matters regardless of background. Most people who develop keloids first notice them in their 20s, with the peak risk window falling between ages 10 and 30. That said, keloids can appear at any age, from infancy to the 70s and beyond. Young women with pierced ears are another commonly affected group.
Genetic research is starting to identify specific genes involved. A large genome-wide study in Europeans found three chromosomal regions linked to excessive scarring. One contains a gene called NEDD4, which appears to influence fibroblast behavior, and another involves a coding variant in a gene called PHLDA3 that increased scarring risk by 46%. These findings point to inherited differences in how fibroblasts regulate collagen production, which helps explain why keloids run so strongly in families. If one or both of your parents developed keloids, your chances are significantly higher.
Where on the Body Keloids Form
Keloids don’t form equally across all skin. The shoulders, upper back, and chest are the most common sites. Earlobes are another frequent location, largely because of how common ear piercings are. The breastbone is a well-known trouble spot for people who’ve had open heart surgery. Areas where skin is under more tension during healing, like the chest and shoulders, tend to be higher risk because the constant pulling may stimulate excess collagen production.
Keloids vs. Hypertrophic Scars
Not every raised scar is a keloid. Hypertrophic scars also appear thick and elevated, but they stay within the boundaries of the original wound. A keloid, by definition, keeps growing and invades the healthy skin surrounding the injury. This horizontal spread beyond the wound’s edges is the defining characteristic.
The growth pattern also differs. A hypertrophic scar eventually plateaus and often starts to flatten and fade on its own over months or years. Keloids show continuous growth with no natural regression phase. They can keep expanding for years, sometimes becoming significantly larger than the injury that caused them. If you have a raised scar that seems to be spreading outward into skin that was never injured, that’s the hallmark of a keloid rather than a normal thick scar.
Reducing Your Risk
If you know you’re prone to keloids, the most effective strategy is avoiding unnecessary skin injuries. The American Academy of Dermatology recommends against body piercings, tattoos, and elective surgeries for people with a keloid history. Even routine skin disruptions like ingrown hairs and minor cuts can set the process in motion, so careful shaving habits and prompt treatment of acne can help lower your exposure to triggers.
For unavoidable injuries or necessary surgeries, early intervention during the healing phase can reduce keloid risk. Pressure garments, silicone sheets, and steroid injections applied during the early wound-healing window are commonly used preventive approaches. The goal is to modulate collagen production before it spirals out of control, which is easier than trying to shrink a keloid once it has fully formed.