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 a raised 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 uncommon reactions to damage. However, a keloid is an abnormal scar that grows beyond the limits of the original site of skin damage.

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

A hypertrophic scar is a widened 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. Similar to keloids, hypertrophic scars are associated with adverse wound healing factors.

There are no particular characteristics that can indicate what will be the ultimate appearance 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 two kinds of excessive scarring observed clinically that need different therapeutic approaches. The clinical course and physical appearance define keloids and hypertrophic scars as different lesions; however, they are usually confused because of an apparent absence of morphologic differences. Still, medical differences between hypertrophic scarring and keloids have long been recognized by plastic surgeons and dermatologists. Yet, translating these differences into morphologic or biochemical distinctions has prompted much conflict in the literature. This report is an attempt to explain the longstanding discussion involving these 2 similar yet individual 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 are chronic deforming dermatoses with a strong resistance to therapy. 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 impairment as much as people with other chronic skin ailments. An item-pool was made changing and supplementing the items of the Questionnaire on Experience with Skin Complaints. This questionnaire was distributed to 100 outpatients with keloids and hypertrophic scarring. A factor analysis was used to recognize the underlying dimensions. Two scales (psychological and physical impairment) of the questionnaire with nine and five items, respectively, were established. Test-retest validity of the questionnaire was excellent (corr>0.9). High 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 relationships were minor. This study demonstrates for the first time an impairment of quality of life in a large group of patients with keloid and hypertrophic scarring.