Keloid scar

by Iris Teo MD FRCPC
December 9, 2024

A keloid scar is an overgrowth of scar tissue that develops after a skin injury, such as a cut, burn, surgical incision, or even a piercing or acne. Unlike normal scars, keloids grow beyond the boundaries of the original wound and may continue to enlarge over time. This happens because the body produces excess collagen, a protein that helps heal wounds, leading to the raised, thickened appearance of the scar.

Keloid scars are noncancerous and harmless, but their appearance can cause discomfort or concern, particularly when located on visible areas like the face, chest, or ears.

What are the symptoms of a keloid scar?

Keloid scars can vary in size, shape, and symptoms.

Common features and symptoms include:

• Appearance: Keloids are raised, thickened scars that can be pink, red, or darker than the surrounding skin. They often have a shiny or smooth surface.
• Growth: They extend beyond the original injury site and can continue to grow over weeks or months.
• Texture: Keloids are typically firm or rubbery to the touch.
• Itching or irritation: Many people with keloids experience itching, tenderness, or a burning sensation, especially during growth.
• Discomfort: If they form near a joint, keloids may cause pain, tightness, or restricted movement in some cases.

What causes a keloid scar?

A keloid scar forms when the body produces too much collagen during the healing process after a skin injury. Collagen is a protein that helps repair damaged skin, but in keloids, the production goes into overdrive, resulting in an excessive buildup of scar tissue. The exact cause of this abnormal response is not fully understood, but it is believed to involve a combination of genetic, cellular, and environmental factors.

What are the risk factors for developing a keloid scar?

Certain factors increase the likelihood of developing a keloid scar, including:

• Genetics: People with a family history of keloid scars are more likely to develop them.
• Skin type: Individuals with darker skin tones, including those of African, Hispanic, or Asian descent, are at higher risk.
• Age: Keloids are more common in younger people, especially between 10 and 30.
• Injury type: Injuries such as cuts, burns, surgical wounds, piercings, tattoos, acne, and even vaccinations can trigger keloid formation.
• Location: Keloids are more likely to develop on specific body parts, such as the chest, shoulders, upper back, earlobes, and cheeks.
• Chronic irritation: Repeated irritation or tension on a healing wound may increase the risk of keloid formation.

What are the microscopic features of a keloid scar?

Under the microscope, a keloid scar has several distinct features:

• Thickened collagen bundles: The scar tissue shows large, disorganized collagen bundles. Unlike normal scar tissue, keloid collagen is arranged in a haphazard, “wavy” pattern.
• Excessive extracellular matrix: Besides collagen, there is an overproduction of other proteins and substances that make up the extracellular matrix, contributing to the scar’s density.
• Sparse inflammatory cells: Unlike early healing wounds, keloids have few inflammatory cells, as they are typically fully matured scars.
• Prominent blood vessels: Increased blood vessels may be visible in some areas, especially during the early stages of keloid formation.
• Thickened epidermis: The skin covering the keloid may appear slightly thickened compared to the surrounding normal skin.

These microscopic features help pathologists distinguish keloids from other types of scars or skin conditions and confirm the diagnosis.