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).
Histamine is a natural chemical produced by the immune (disease-fighting) system of the body. When it is released, it increases blood flow to the affected area. Liquid leaks out of the blood vessels, making the mucous membranes lining the nose and throat to swell, and stimulating nearby gland to produce mucus.