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What are hypertrophic scars and keloids after burn injuries?

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Cross-section diagram of human skin showing burn depth by degree, with arrows indicating that first-degree burns affect only the epidermis, second-degree burns reach the dermis, third-degree burns extend into subcutaneous tissue, and fourth-degree burns penetrate to muscle. — burn This diagram shows how burn injuries are classified by severity. First-degree burns damage the outer skin, known as the epidermis. First-degree burns are the least severe form of burn injury. Second-degree burns damage the outer skin and some of the underlying skin, known as the dermis, which also includes some connective tissue. Third-degree burns damage all the layers of skin, including subcutaneous tissue. Fourth-degree burns, which are the most severe, destroy every layer of skin and also damage muscle, tendons, and bones.

After a burn injury, the skin's healing process can sometimes result in excessive scar tissue formation. Two primary types of overscarring are keloids and hypertrophic scars.1

Hypertrophic Scars

Hypertrophic scars occur when the body produces an excess of fibrous collagen during healing. While these scars become overly thick, they remain confined within the original boundaries of the burn wound.1

Keloids

Keloids are benign, tumorlike growths that result from an uninhibited and excessive wound-healing response. Unlike hypertrophic scars, keloids extend beyond the limits of the original wound. They often appear as smooth, rubbery nodules and can cause pain, itching, or a burning sensation.12

Both types of scarring are particularly problematic when they result from serious burns and cover large areas, as they may restrict movement, especially near joints. Because these scars lack the oil glands and elastic tissue of normal skin, they are often prone to irritation. Furthermore, all scars, particularly those from untreated third-degree burns, carry a risk of malignant change.1