Over 100 million people in the western world alone get scars on their skin after operations or other trauma. Everyone recognizes scars after burns and their reasons are well-known. The difference between keloid and hypertrophic scars is not so easy to recognize.
In general hypertrophic scars are limited to the wound area of the skin and keloid scars can grow outside of the border of the wounded areas and grow to cover large areas of the skin.
Hypertrophic scars normally appear 4 – 8 weeks after the irritation (infection, closing of the wound, trauma to the skin). Then there is a growth phase of one to six months and after that the scar normally decreases in size over several years to become a flat, symptomless unremarkable scar. It consists of collagen fibres which run parallel to the epidermis. Hypertrophic scars appear in 40-70% of patients after surgical intervention and in 91% after burns, depending on the depth of the injury. Scientific studies showed that certain hormones could also increase the growth therefore we can say that people in adolescence or in pregnancy are more vulnerable.
In contrary keloids can grow for several years. The cause could be only little insignificant injuries or even spontaneous appearance without any previous stimulation. Keloids are much more persistent, exist longer and do not regress spontaneously. An increased frequency in people with blood group A has been observed. More than 50% of keloid patients have a genetic predisposition. A keloid consists also in an overproduction of keloid fibres, but they are much more disordered.
Both scars produce too much protein, so called fibroblasts. The reason for their incidence is either a pathological prevention/disturbance of the wound healing or a missing healing interruption.