A scar is the end result of human wound healing. A wound can be created by any injury. Common injuries which cause wounds include burns, cuts to the skin as occur after any operation, inflammation and infection. Sometimes the damage can be quite small, as for example with keloid scars after ear piercing or having a vaccination jab. Once the skin has been damaged, chemical signals are immediately produced at the site. These attract successive waves of cells that are involved with the process of inflammation. The first cells to arrive attack invading bacteria and other organisms. With time, a second set of cells arrive that produce further chemical attractant signals. Eventually after the early inflammation, fibroblast cells arrive in the wound which are the key cells involved in laying down scar tissue.
The amount of inflammation that was present in the early wound largely determines how many fibroblast cells arrive and how busy they become. If the early wound was very inflamed, for example, as a result of infection, many more fibroblasts enter the wound and these produce much more of the connective tissue of a mature scar, largely collagen. However, the amount of inflammation is not the only factor that determines the amount of scar tissue that is formed. Some people’s genes – the genetic code in their DNA that is unique to them – gives them fibroblast cells which are more active than the rest of the population. These cells produce much more collagen for a given amount of stimulation. Other factors determining the amount of inflammation and how active the fibroblast become include your age, background health conditions such as diabetes, site on the body surface and importantly, tension within the skin.
Fibroblasts lay down scar tissue and like sculptors, remodel their work with time. The initial strands of collagen are woven into bigger bundles and the type of collagen is made more resilient with time. Much of the activity of the fibroblasts is in response to the stresses across the developing scar. For reasons not fully know, some fibroblasts develop little muscles which pull on the surrounding collagen like a ‘tug-of-war’. This has the effect of putting tension on the scar and shortening it. However, at its extreme, it can also produce tight bands of scar tissue that limit the range of motion of a joint – contractures.