Regeneration and Repair Mechanisms
The skin has several regeneration and repair mechanisms to eliminate any damage caused by external influences and restore lost function.
Regeneration following UV-induced damage
Intense UV-exposure causes primary damage to the genetic material. Secondary damage is inflicted on the cell proteins and membranes by UV-induced free radicals (i). The skin is known to have many mechanisms for the repair of damaged DNA. In humans the most important are the excision repair and post-replication repair mechanisms: The excision repair mechanism is based on recognition, removal and replacement of the damaged DNA segment.
In this way mutations are prevented as long as the repair mechanism is not overburdened or defective. The post-replication repair mechanism, on the other hand, initially works around the damaged DNA segment, meaning the damage is ignored when the genetic code is read. Only later is the damage repaired. This mechanism is so faulty, however, that often more mutations are caused by the repair than by the original radiation damage.
Regeneration following skin injury
The layer of epidermal mother cells - the basal layer - ensures a steady renewal of the epidermis through continual cell division (proliferation). If an injury is confined to the uppermost skin layer, this damage, which is known as erosion, can heal without scarring. If the damage reaches the dermis (e.g. an ulcer) and thus involves the basal membrane, then healing is usually accompanied by scar formation. In this case destroyed skin cells are replaced by connective tissue. Wound healing takes place in several consecutive stages: in the first stage coagulating blood forms a membrane with a hard surface that adheres to the wound (crust). In the following skin cleansing stage, autolysis and phagocytosis (i) of damaged and dying cells take place. At the same time connective tissue fibres are dissolved by enzymes. This activates mobile immune cells, and phagocytes and lymphatic fluids flow into the wound.
In the tissue building or proliferation phase, epithelisation of the wound base occurs, including the formation of capillary buds, new connective tissue and collagen fibres. Cell division during the proliferation phase can be stimulated and supported by the application of topicals such as dexpanthenol. This is conducive to better and faster healing.