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 body, but some areas like the chest, knees and elbows are more likely to scar.

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

Keloids have the clinical appearance of an elevated amorphous growth and are frequently associated 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 an engrossed or unattractive 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 then stabilize or regress. Similar to keloids, hypertrophic scars are associated with negative wound healing factors.

There are no certain signs that can reveal what will be the ultimate appearance 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 genes, 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 course and physical appearance define keloids and hypertrophic scars as different entities; however, they are usually confused because of an apparent absence of morphologic differences. Still, clinical differences between hypertrophic scarring and keloids have long been recognized by plastic surgeons and dermatologists. Yet, translating these differences into morphologic or biochemical signs has prompted much conflict in the literature. The present report is an attempt to clarify the longstanding discussion involving these 2 similar yet separate and nonidentical entities by highlighting 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 represent chronic disfiguring dermatoses with a strong resistance to treatment. The objective of our study was to assess 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 modifying and supplementing the items of the Questionnaire on Experience with Skin Complaints. The questionnaire was given to one hundred outpatients with keloids and hypertrophic scarring. A factor analysis was used to recognize the underlying dimensions. Two scales (psychological and physical deprivation) of the questionnaire with 9 and 5 items, respectively, were used. Test-retest validity of the questionnaire was excellent (corr>0.9). Good validity was suggested by the correlation of physical deprivation with pain (P less or equal to 0.001), pruritus (P less than 0.001), and the amount of impediment of mobility (P less than 0.001). The psychological scale was associated with pain and impediment of mobility, although the relationships were minor. This study shows for the first time an impairment of quality of life in a large group of patients with keloid and hypertrophic scars.