Wounds heal in three stages.
Inflammation is when blood clots form, bacteria are attacked to prevent infection, and key biochemical cells gather at the site of the wound, causing it to swell. Inflammation begins almost immediately after injury, peaking at three to five days.
Then there is proliferation, when these key cells multiply at the wound site to make new tissue and blood vessels. Open wounds generally heal from the bottom up, as cells multiply to fill in the wound with new tissue.
Finally, there is the remodeling phase, where the wound is healed and the initial scar tissue is gradually restructured.
There are many different types of cells involved in the healing process, including platelets, macrophages and fibroblasts. Platelets are the first to arrive at the wound site and release growth factors: proteins that allow cells to communicate with each other. The growth factors are essential to the healing process. They attract other useful cells and proteins to the wound site, including immune cells to ward off infection, and stimulate and increase the production of connective tissue. They also create a new supply of blood vessels to nourish the wound site, and promote new skin growth across the open area of the wound.