U01.04.019 Scar formation

Scar formation occurs when tissue repair cannot be achieved through cell regeneration alone. Non-regenerated cells, often due to severe acute or chronic injury, are replaced by connective tissue. Although 70–80% of tensile strength is regained in 3 months, only minimal additional strength is regained afterward. Scar formation is often associated with excess TGF-β.

Types of Scars

Scar Type	Hypertrophic	Keloid
Collagen Synthesis	Predominantly type III collagen	Types I and III collagen
Collagen Organization	Parallel organization	Disorganized
Extent of Scar	Confined to the borders of the original wound	Extends beyond the borders of the original wound, often with “claw-like” projections on earlobes, face, and upper extremities
Recurrence	Infrequent	Frequent
Predisposition	None	More common in ethnic groups with darker skin

Types of Scars

Points to Remember

Scar formation is a process that replaces non-regenerated cells with connective tissue when cell regeneration is not sufficient.
Hypertrophic scars generally have parallel collagen fibers and are limited to the wound’s original borders.
Keloid scars have disorganized collagen fibers and can extend beyond the original wound, often with pronounced projections.
Hypertrophic scars rarely recur, while keloids are prone to frequent recurrence.
Keloid formation is more common in individuals with darker skin tones.

USMLE Step 1 Review Series

Curriculum

U01.04.019 Scar formation

Types of Scars

Points to Remember

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