Last updated: Sun, Jun 18, 2017
If the injury is bad enough, the area along the scratch will become more pale and begin to swell. The chemicals released by injury have triggered an inflammatory reaction. The local blood vessels begin to leak fluid from the blood into the area of the wound, which accounts for the wheal. The chemicals spilled during the initial injury cause special immune cells in the skin called mast cells to break down, which adds histamines and other chemicals to the mix. The neurons which were activated by the scratch add chemicals of their own. The injury is now hot and achy.
Inflammation is a powerful booster of pain. The painfulness of sore throat, arthritic joints, and sunburn are all largely the result of inflammation.
The inflammatory reaction is meant to limit damage and promote healing. The chemicals attract immune cells that clean up cellular debris and control pathogens. They also attract fibroblasts, cells that generate the fibrous material that is used to perform initial tissue repairs.