A keloid is an abnormal proliferation of scar tissue that forms at the site of cutaneous injury (eg, on the site of a surgical incision or trauma); it does not regress and grows beyond the original margins of the scar. Keloids should not be confused with hypertrophic scars, which are raised scars that do not grow beyond the boundaries of the original wound and may reduce over time.
Keloids can form after skin injuries from:
- Ear piercing
- Minor scratches
- Cuts from surgery or trauma
- Vaccination sites
The problem is more common in people ages 10 to 20, and in African Americans, Asians, and Hispanics. Keloids often run in families.
Keloids are dermal fibrotic lesions that are a variation of the normal wound healing process. They usually occur during the healing of a deep skin wound. Hypertrophic scars and keloids are both included in the spectrum of fibroproliferative disorders. These abnormal scars result from the loss of the control mechanisms that normally regulate the fine balance of tissue repair and regeneration.
The excessive proliferation of normal tissue healing processes results in both hypertrophic scars and keloids. The production of extracellular matrix proteins, collagen, elastin, and proteoglycans presumably is due to a prolonged inflammatory process in the wound. Hypertrophic scars are raised, erythematous, fibrotic lesions that usually remain confined within the borders of the original wound. These scars occur within months of the initial trauma and have a tendency to remain stable or regress with time.
Keloid formation can occur within a year after injury, and keloids enlarge well beyond the original scar margin. The most frequently involved sites of keloids are areas of the body that are constantly subjected to high skin tension. Wounds on the anterior chest, shoulders, flexor surfaces of the extremities (eg, deltoid region), and anterior neck and wounds that cross skin tension lines are more susceptible to abnormal scar formation.
The most important risk factor for the development of abnormal scars such as keloids is a wound healing by secondary intention, especially if healing time is greater than 3 weeks. Wounds subjected to a prolonged inflammation, whether due to a foreign body, infection, burn, or inadequate wound closure, are at risk of abnormal scar formation. Areas of chronic inflammation, such as an earring site or a site of repeated trauma, are also more likely to develop keloids. Occasionally, spontaneous keloids occur without a history of trauma.
After the initial insult to the skin and the formation of a wound clot, the balance between granulation tissue degradation and biosynthesis becomes essential to adequate healing. Extensive studies of the biochemical and cellular composition of keloids compared to mature scar tissue demonstrate significant differences. Keloids have an increased blood vessel density, higher mesenchymal cell density, a thickened epidermal layer, and increased mucinous ground substance. The alpha–smooth muscle actin fibroblasts, myofibroblasts important for contractile situations, are few, if present at all.
The collagen fibrils in keloids are more irregular, abnormally thick, and have unidirectional fibers arranged in a highly stressed orientation.Biochemical differences in collagen content in normal hypertrophic scars and keloids have been examined in numerous studies. Collagenase activity, ie, prolyl hydroxylase, has been found to be 14 times greater in keloids than in both hypertrophic scars and normal scars. Collagen synthesis in keloids is 3 times greater than in hypertrophic scars and 20 times greater than in normal scars. Type III collagen, chondroitin 4-sulfate, and glycosaminoglycan content are higher in keloids than in both hypertrophic and normal scars. Collagen cross-linking is greater in normal scars, while keloids have immature cross-links that do not form normal scar stability.
The increased numbers of fibroblasts, recruited to the site of tissue damage, synthesize an overabundance of fibronectin, and receptor expression is increased in keloids. Mast cell population within keloid scars is also increased, and, subsequently, histamine production increases.
A keloid may be:
- Flesh-colored, red, or pink
- Located over the site of a wound or injury
- Lumpy (nodular) or ridged
- Tender and itchy
- Irritated from friction such as rubbing on clothing
A keloid will tan darker than the skin around it if exposed to sun during the first year after it forms. The darker color may not go away.
Keloids can be diagnosed by your doctor or dermatologist (skin specialist). Diagnosis is based on the location and appearance of the scar, and how it progresses over time. Your doctor may do a physical exam and look at your medical and personal history to rule out any other possible diseases or conditions.
Keloids often do not need treatment. If the keloid bothers you, the following things can be done to reduce the size:
- Corticosteroid injections
- Freezing (cryotherapy)
- Laser treatments
- Surgical removal
- Silicone gel or patches
Many of these treatments can cause a larger keloid scar to form.