When a scar is thickened, it does not invade healthy 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 a raised scar and invades healthy tissue, then it is called a keloid scar. All types of scarring can occur 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 responses 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 look of an elevated amorphous growth and are frequently associated with pruritus and pain. Microscopy analysis reveals randomly disposed collagen fibers in a dense connective tissue matrix, making keloid removal a difficult task. In normal scars, the collagen bundles are disposed parallel to the skin surface.

A hypertrophic scar is an engrossed or unattractive scar that does not extend beyond the original boundaries 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 associated with negative wound healing factors.

There are no particular characteristics that can reveal what will be the ultimate look of a scar or what kind of scar it will be. The way in which a wound cures 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 excessive scarring observed clinically that need different therapeutic approaches. The clinical course and physical look define keloids and hypertrophic scars as separate lesions; however, they are usually confused because of an apparent absence of morphologic differences. Nevertheless, clinical differences between hypertrophic scars and keloids have long been recognized by plastic surgeons and specialists. Yet, expressing these differences into morphologic or biochemical distinctions has created much conflict in the literature. The present report is an attempt to explain the longstanding discussion regarding these 2 similar yet separate and nonidentical entities by explaining 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 deforming dermatoses with a strong resistance to therapy. The aim of our study was to assess for the first time the quality of life of people with hypertrophic scars and keloids, because they suffer from quality of life impairment as much as people with other chronic skin ailments. An item-pool was made changing and complementing the items of the Questionnaire on Experience with Skin Complaints. This questionnaire was distributed to one hundred outpatients with keloids and hypertrophic scars. A factor analysis was used to identify the underlying dimensions. Two scales (psychological and physical impairment) of the questionnaire with 9 and 5 items, respectively, were established. Test-retest reliability of the questionnaire was excellent (corr>0.9). Good validity was proposed by the correlation of physical impairment 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 associated with pain and impediment of mobility, although the correlations 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 scarring.