Keloids are the result of an overgrowth of dense fibrous tissue that usually develops after healing of a skin injury. The tissue extends beyond the borders of the original wound, does not usually regress spontaneously, and tends to recur after excision. The first description of keloids (recorded on papyrus) concerned surgical techniques used in Egypt in 1700 BCE. Subsequently, in 1806, Alibert used the term cheloide, derived from the Greek chele, or crab's claw, to describe the lateral growth of tissue into unaffected skin. Note the image below.
In contrast, hypertrophic scars are characterized by erythematous, pruritic, raised fibrous lesions that typically do not expand beyond the boundaries of the initial injury and may undergo partial spontaneous resolution. Hypertrophic scars are common after thermal injuries and other injuries that involve the deep dermis.
See 5 Body Modifications and Piercing: Dermatologic Risks and Adverse Reactions, a Critical Images slideshow, to help recognize various body modifications and the related potential complications.
Related articles include Laser Treatment of Scars and Stria Distensae, Keloids, and Widened and Hypertrophic Scar Healing.
Hypertrophic scars and keloids can be described as variations of typical wound healing. In a typical wound, anabolic and catabolic processes achieve equilibrium approximately 6-8 weeks after the original injury. At this stage, the strength of the wound is approximately 30-40% that of healthy skin. As the scar matures, the tensile strength of the scar improves as a result of progressive cross-linking of collagen fibers. At this point, the scar is usually hyperemic and it may be thickened, but it tends to subside gradually over months until a flat, white, pliable, possibly stretched, mature scar has developed. When an imbalance occurs between the anabolic and catabolic phases of the healing process, more collagen is produced than is degraded, and the scar grows in all directions. The scar is elevated above the skin and remains hyperemic. Excessive fibrous tissue is classified as either a keloid or a hypertrophic scar.
Kischer and Brody declared the collagen nodule to be the identifying structural unit of hypertrophic scars and keloids.  The nodule, which is absent from mature scars, contains a high density of fibroblasts and unidirectional collagen fibrils in a highly organized and distinct orientation. In addition, keloids and hypertrophic scars differ from healthy skin by a rich vasculature, high mesenchymal cell density, and thickened epidermal cell layer. Attempts to clinically differentiate keloids from hypertrophic scars have proved to be difficult in the early phases of formation. Clinical differences become more apparent as lesions mature. The most consistent histologic difference is the presence of broad, dull, pink bundles of collagen (hyalinized bundles of collagen) in keloids, which are not present in hypertrophic scars.
Only humans are affected by keloids, and both dominant and recessive modes of inheritance have been described. Although keloids occur in all age groups, they are rarely found in newborns or elderly persons and have the highest incidence in individuals aged 10-20 years.
Keloids form more frequently in Polynesian and Chinese persons than in Indian and Malaysian persons. As many as 16% of people in a random sampling of black Africans reported having keloids. White persons are least commonly affected.
The prevalence has been reported to be higher in young females than in young males, probably reflecting the greater frequency of earlobe piercing among females. Keloids and hypertrophic scars affect both sexes equally in other age groups.
Onset occurs most commonly in individuals aged 10-30 years. Keloids occur less frequently at the extremes of age, although an increasing number of presternal keloids have resulted from coronary artery bypass operations and other similar procedures now undertaken in persons in older age groups.
Keloids rarely resolve spontaneously; however, with treatment, they may become softer, less tender, less painful, and less pruritic. Following excision treatment alone, keloids frequently recur (>50%).
Keloids and hypertrophic scars located at most sites are primarily of cosmetic concern; however, some keloids or hypertrophic scars can cause contractures, which may result in loss of function if overlying a joint or in significant disfigurement if located on the face.
Keloids and hypertrophic scars are associated genetically with HLA-B14, HLA-B21, HLA-Bw16, HLA-Bw35, HLA-DR5, HLA-DQw3, and blood group A.
Advise patients to avoid local skin trauma (eg, skin piercing, tattoos) and to control inflammatory acne. Initially, focus is placed on the alleviation of symptoms.
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