of, relating to, or of the nature of preference: preferential policies. 2. showing or giving preference: a preferential hiring system. 3. receiving or enjoying preference, as a country in trade relations; favored. Origin of preferential.
Histamine dilates post-capillary venules, activates the endothelium, and increases blood vessel permeability. This leads to local edema (swelling), warmth, redness, and the attraction of other inflammatory cells to the site of release. It also depolarizes nerve endings (leading to itching or pain).
The release of histamine and its effects on the tissue are part of the body's defenses. Dilating blood vessels near the site of an injury reduces blood flow, and therefore blood loss, in the area. Capillary permeability allows white blood cells to pass into the tissue, where they can begin the healing process.