When a scar is thickened, it doesn't invade normal tissue and lies across the relaxed skin tension lines (creases in the skin). This type of scar falls into the 'hypertrophic' category.

In the case that it is an elevated scar and invades normal tissue, then it is called a keloid scar. All kinds of scarring can appear on different areas of the skin, but some areas like the chest, knees and elbows are more likely to scar.

Both keloid and hypertrophic scar tissues are atypical reactions to trauma. However, a keloid is an aberrant scar that grows beyond the boundaries of the original site of skin damage.

Keloids have the clinical appearance of an elevated amorphous growth and are usually linked with pruritus and pain. Microscopy observation reveals randomly disposed collagen fibers in a dense connective tissue matrix, making keloid removal a difficult task. In normal scarring, the collagen bundles are arranged parallel to the skin surface.

A hypertrophic scar is a widened or unsightly scar that does not grow beyond the original boundaries of the wound. Unlike keloids, scars caused by hypertrophic actinic keratosis reach a certain size and subsequently stabilize or regress. Like keloids, hypertrophic scars are linked with adverse wound healing factors.

There are no particular characteristics that can reveal what will be the ultimate appearance of a scar or what type of scar it will be. The way in which a wound cures is different for every person and is determined by genetics, the environment and how you care for it.

Keloid or hypertrophic scar: A review of the literature

Atiyeh BS, Costagliola M, Hayek SN.

Division of Plastic and Reconstructive Surgery, American University of Beirut Medical Center, Beirut, Lebanon.

Keloid and hypertrophic scars are 2 kinds of exaggerated scarring observed clinically that need different treatment approaches. The clinical signs and physical appearance define keloids and hypertrophic scars as different lesions; however, they are often confused because of an apparent absence of morphologic differences. Still, clinical differences between hypertrophic scarring and keloids have long been known by plastic surgeons and specialists. Yet, expressing these differences into morphologic or biochemical distinctions has prompted much conflict in the literature. This report is an attempt to clarify the longstanding controversy regarding these 2 similar yet individual and nonidentical entities by explaining the reported points of differentiation as well as the similarities.

Quality of life of patients with keloid and hypertrophic scarring.

Bock O, Schmid-Ott G, Malewski P, Mrowietz U.

Primary Health Care Center, Halsan 2, Fabriksgatan 17, 55 185, Jonkoping, Sweden.

Keloid and hypertrophic scarring are chronic deforming dermatoses with a strong resistance to treatment. The objective of our study was to evaluate for the first time the quality of life of people with hypertrophic scarring and keloids, because they suffer from quality of life deprivation as much as people with other chronic skin ailments. An item-pool was created modifying and complementing the items of the Questionnaire on Experience with Skin Complaints. The questionnaire was given to 100 outpatients with keloids and hypertrophic scarring. A factor analysis was used to identify the underlying dimensions. Two scales (psychological and physical deprivation) of the questionnaire with 9 and 5 items, respectively, were established. Test-retest reliability of the questionnaire was excellent (corr>0.9). High validity was proposed by the correlation of physical deprivation with pain (P less or equal to 0.001), pruritus (P less than 0.001), and the proportion of restriction of mobility (P less than 0.001). The psychological scale was linked with pain and restriction of mobility, although the relationships were minor. This study demonstrates for the first time a deprivation of quality of life in a large group of sufferers with keloid and hypertrophic scars.