A scar is an undesirable, yet normal consequence of wound healing. To understand how they are formed, it is key to understand a little bit about the skin and how it heals after damage.
Layers of the skin
The skin consists of three layers. From outside in, these layers are the epidermis, the dermis and the subcutis. The epidermis provides the first barrier against infection, and it also regulates the amount of water released from the body.
The dermis lies below, and gives the skin its flexibility and strength due to special proteins like collagen and elastin. But the dermis also contains nerve endings, sweat glands, sebaceous glands, hair follicles and blood vessels. Because of all these different components, the dermis can support the epidermis. The dermis is it also responsible for body temperature regulation and the sensations you feel, like pressure, heat and pain.
Finally, there is the innermost layer of the skin, the subcutis. This layer primarily contains fat and connective tissue, which makes it the insulation layer that helps maintain body temperature in cold environments. The fat also helps protecting the internal organs, muscles and bones from external trauma. Finally, a lot of nerves and blood vessels run through the subcutis on their way to muscles or the outer skin layers.
What happens when the skin gets damaged?
If a wound extends deep into the dermis or even into the subcutaneous tissue below that, it results in more severe scars. It is the result of skin wound healing, a complex process consisting of three phases.
Phase one: inflammation
Directly after the skin suffers injury, hemostasis or blood clotting will occur. The main goal of hemostasis is to prevent excessive bleeding. The blood clot that is formed will release proteins called growth factors. These will attract several types of inflammatory cells, initiating the inflammation phase. The aim of this phase is wound debridement: micro-organisms are killed and dead tissue removed by activated inflammatory cells such as macrophages, neutrophils and lymphocytes. The inflammation process attracts other types of cells to the site, such as fibroblasts and keratinocytes.
Phase two: proliferation
Fibroblasts and keratinocytes are key players in the second phase: the proliferation phase. During the proliferation phase, the wound is covered with new tissue made of collagen and extracellular matrix. Additionally, new blood vessels are created to supply the new tissue.
Phase three: maturation
The next and final phase is the remodeling or maturation phase. This phase starts when the wound is closed and may last up to one or two years. During this period, the new tissue (created in the proliferation phase) is changed, reorganized and aligned. The cells that helped repairing the wound are removed by apoptosis: controlled and programmed cell death. From the outside the scar will visibly ‘calm down’ and look less thick and red.
Gaining insight in the subsequent phases of wound healing helps us to understand the various ways we can promote the most favorable scar formation. Accurate wound care encourages and accelerates wound healing.
In 2017, we started the development of the POSAS 3.0. This version can be used to measure scar quality in patients with all types of scars, including those caused by burns, necrotizing fasciitis, acne, trauma, or surgery. In this project, we have involved many relevant stakeholders, including patients, as well as a broad range of professional experts.
Expected in 2022
Currently we are testing the measurement properties of the POSAS 3.0. POSAS 3.0 will be launched at ISBI 2022!