When a scar is thickened, it doesn't invade normal tissue and lies across the normal 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 types 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 uncommon reactions to damage. However, a keloid is an aberrant scar that grows beyond the limits of the original site of skin injury.

Keloids have the clinical look of a raised amorphous growth and are usually linked with pruritus and pain. Microscopy analysis shows randomly disposed collagen fibers in a hard 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 extend beyond the original limits of the wound. Unlike keloids, scars caused by hypertrophic actinic keratosis grow to a certain size and then stabilize or regress. Like keloids, hypertrophic scars are linked with adverse wound healing factors.

There are no certain signs that can indicate what will be the ultimate look of a scar or what kind of scar it will be. The way in which a wound heals 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 types of exaggerated scarring observed clinically that require different treatment approaches. The clinical signs and physical look define keloids and hypertrophic scars as different entities; however, they are usually confused because of an apparent lack of morphologic differences. Still, medical differences between hypertrophic scarring and keloids have long been known by plastic surgeons and dermatologists. Yet, translating these differences into morphologic or biochemical distinctions has prompted much conflict in the literature. The present report is an attempt to clarify the longstanding controversy involving these 2 similar yet separate and nonidentical entities by highlighting the reported points of individualization 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 therapy. The aim 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 diseases. An item-pool was created changing and supplementing 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 nine and five items, respectively, were established. Test-retest reliability of the questionnaire was excellent (corr>0.9). Good 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 impediment of mobility (P less than 0.001). The psychological scale was linked with pain and impediment of mobility, although the relationships were lower. This study shows for the first time an impairment of quality of life in a large group of sufferers with keloid and hypertrophic scars.