When a scar is thickened, it does not invade healthy 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 healthy tissue, then it is called a keloid scar. All kinds 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 uncommon responses to damage. However, a keloid is an aberrant scar that grows beyond the limits of the original site of skin damage.

Keloids have the clinical appearance of an elevated amorphous growth and are frequently 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 scars, 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 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 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 heals is different for every individual 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 two kinds of excessive scarring observed clinically that require different treatment approaches. The clinical course and physical appearance define keloids and hypertrophic scars as separate lesions; however, they are usually confused because of an apparent absence of morphologic differences. Still, clinical differences between hypertrophic scars and keloids have long been known by plastic surgeons and dermatologists. Yet, expressing these differences into morphologic or biochemical signs 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 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 represent chronic disfiguring dermatoses with a high resistance to treatment. The aim of our research was to evaluate for the first time the quality of life of patients with hypertrophic scars and keloids, because they suffer from quality of life deprivation as much as patients with other chronic skin diseases. An item-pool was made changing and complementing the items of the Questionnaire on Experience with Skin Complaints. The questionnaire was distributed to 100 outpatients with keloids and hypertrophic scars. 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 established. Test-retest validity of the questionnaire was excellent (corr>0.9). High 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 linked with pain and impediment of mobility, although the correlations were minor. This research demonstrates for the first time an impairment of quality of life in a large group of sufferers with keloid and hypertrophic scars.