The region below the unjulating line is the dermis, above is the epidermis. The scars are characterised by excess collagen deposition. They are clinically difficult to distinguish and although hypertrophic lesions generally regress, keloids do not and currently no effective treatment exists. It has a raised appearance and is confined to the region of the original injury. They extend beyond the confines of the original wound, and frequently reoccur after treatment.
Nitric oxide is a free radical molecule.
It has commonly been labelled as an environmental pollutant, present, for example in acid rain. However, in the 1980's it was discovered that it is widely synthesised by mammalian cells, and has many roles, including one in wound healing. Upon wounding, fibroblasts and other cells synthesise nitric oxide which acts as a vasculodilator and also stimulates fibroblasts to produce collagen.