Hypertrophic scars form when the body’s wound-healing process overreacts, producing too much collagen at the injury site. Unlike normal scars that flatten over time, hypertrophic scars remain raised, firm, and sometimes itchy or painful. The core problem is a disruption in the balance between collagen production and collagen breakdown during healing, driven by prolonged inflammation, excess signaling proteins, and mechanical stress on the wound.
How Normal Healing Goes Wrong
When skin is injured, the body launches a repair sequence: inflammation clears debris, new blood vessels form, and specialized cells called fibroblasts lay down collagen to close the wound. In normal healing, this collagen is eventually remodeled into a flat, pale scar. In hypertrophic scarring, fibroblasts become overactive and transform into a more aggressive cell type that contracts tissue and keeps depositing collagen long after the wound has closed.
A key signaling protein called TGF-beta drives much of this overproduction. TGF-beta promotes the creation of collagen and other structural proteins, stimulates fibroblast multiplication, and triggers fibroblasts to transform into their more aggressive form. In hypertrophic scars, TGF-beta signaling stays elevated instead of tapering off as it should. This sustained signal keeps the wound in a building phase, resulting in thick, raised scar tissue packed with excess collagen and fibrous protein.
The mechanism of hypertrophic scar formation is also tied to abnormal activation of genes involved in producing structural proteins like collagen types I and III, fibronectin, and a contractile protein found in these transformed fibroblasts. Together, these molecules create a dense, disorganized matrix that gives hypertrophic scars their characteristic firmness and elevation above the surrounding skin.
The Role of Prolonged Inflammation
A prolonged inflammatory phase is one of the strongest drivers of hypertrophic scarring. When inflammation lingers in the deeper layers of the skin, it triggers abnormal blood vessel growth, which in turn extends the inflammatory cycle further. The excessive release of inflammatory cells and signaling molecules disrupts normal fibroblast function and pushes the wound toward pathological scarring instead of orderly repair.
Anything that delays the wound from closing its surface layer of skin increases the risk. A delayed closure interferes with the resolution of the temporary tissue that fills the wound gap, leaving behind higher amounts of collagen and contractile cells than a wound that heals on schedule. Wound infections, repeated trauma to the healing site, and burns that destroy deeper skin layers all contribute to this kind of delay.
Mechanical Tension on the Wound
Physical tension across a healing wound is one of the most important and underappreciated causes of hypertrophic scarring. When skin is pulled or stretched around a wound, the mechanical stress prolongs and intensifies inflammation in the deeper skin layers. This repeated strain leads to abnormal blood vessel growth and pushes fibroblasts into overdrive.
The contractile fibroblasts in the wound respond to both chemical signals like TGF-beta and physical stress. As they contract the collagen network, they generate additional mechanical pressure within the scar itself, creating a feedback loop: tension triggers more collagen production, which stiffens the tissue, which increases tension. Clinical evidence and animal studies consistently show that increased tension leads to more severe scar buildup. This is why wounds that cross joints or sit on areas of frequent movement are especially prone to hypertrophic scarring.
Body Areas Most at Risk
Hypertrophic scars tend to develop in predictable locations, almost all of which are high-tension areas. The shoulders, neck, front of the chest, knees, and ankles are the most common sites. These areas experience constant pulling from movement, posture, and the natural tension lines of the skin.
By contrast, some body areas rarely develop hypertrophic scars. The eyelids, palms, soles of the feet, mucous membranes, and genitalia are much less affected. The cornea is similarly resistant. The difference comes down to the mechanical environment and the structure of the skin in these regions. For people recovering from burns, the neck, chest, and upper limbs carry the highest risk of hypertrophic scarring.
Who Is More Likely to Develop Them
Several personal factors influence your risk. Younger people, particularly those under 30, are significantly more prone to hypertrophic scarring. This likely reflects more vigorous inflammatory and healing responses in younger skin. Interestingly, people over 55 tend to heal with less scarring, and their scars mature faster.
Skin color plays a role as well. People with darker skin tones, specifically Fitzpatrick skin types IV through VI, face higher rates of hypertrophic scarring. The condition is more prevalent among Black/African American and Asian patients. Female sex has also been identified as a risk factor, as has the total percentage of body surface area affected in burn injuries. The larger the burn, the greater the chance of developing raised scars.
How Hypertrophic Scars Differ From Keloids
Hypertrophic scars and keloids are often confused because both are raised, firm, and caused by excess collagen. But they behave differently in ways that matter for treatment and expectations. A hypertrophic scar stays within the borders of the original wound. A keloid, by definition, extends beyond the original injury site and can even form spontaneously without an obvious wound. If a raised scar hasn’t spread past the edges of your original cut, burn, or incision, it’s a hypertrophic scar, not a keloid.
The other critical difference is trajectory. Hypertrophic scars can regress over time, gradually flattening and softening. Keloids do not regress on their own. Hypertrophic scars are also considerably more common than keloids. Both can be itchy, painful, and restrict movement depending on their size and location, but their long-term behavior and treatment approaches differ significantly.
How Long Maturation Takes
Hypertrophic scars take much longer to fully mature than most people expect. A retrospective study of 361 hypertrophic scars tracked over five years found that the average maturation time for patients under 30 was nearly 36 months. For patients between 30 and 55, it was about 35 months. Older patients over 55 matured fastest, at roughly 22.5 months, but even that is close to two years.
These numbers are significantly longer than earlier estimates suggested. Maturation means the scar has stopped changing: it has softened, flattened as much as it will, and the redness has faded. Understanding this timeline matters because it influences decisions about when to pursue treatment and helps set realistic expectations. A scar that still looks raised and red at 12 months may still improve considerably on its own over the following one to two years.
Common Triggers
Almost any skin injury can trigger a hypertrophic scar in a susceptible person, but some wounds carry higher risk than others:
- Burns: Especially deep partial-thickness and full-thickness burns, which destroy enough skin layers to guarantee prolonged healing and inflammation.
- Surgical incisions: Particularly those crossing joints or high-tension areas, or wounds that are closed under tension.
- Traumatic wounds: Lacerations, abrasions, and other injuries that cause irregular tissue damage and slower healing.
- Piercings and vaccinations: Even small puncture wounds can trigger hypertrophic scarring in the right location and in susceptible individuals.
- Infected wounds: Any infection that prolongs the inflammatory phase and delays surface closure increases risk substantially.
The common thread across all these triggers is the same: anything that extends inflammation, delays wound closure, or increases mechanical stress on the healing tissue pushes the body’s repair system past its normal limits and into the territory of excessive scarring.