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 produces common allergy symptoms such as itchy, watery eyes, nasal and sinus congestion, headaches, sneezing, scratchy throat, hives, shortness of breath, etc. Other less common symptoms are balance disturbances, skin irritations such as eczema, and even respiratory problems like asthma.