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).
On a general level, histamine is a chemical neurotransmitter produced by the body during an allergic reaction, most noticeably causing skin, nose, throat and lung irritation (itchiness, redness, swelling, rash, cough and flem, mucosa) in response to various allergens: insect bites or topical irritants, dust pollen, food allergies.