Now, what the histamine and these other chemicals do is they initiate an inflammation response and that dilates the blood vessels that carry blood to this area, to this infected area. So we say infected because this otherwise non harmful foreign substance was labeled as pathogenic by our immune system. And so this technically is an infected area to that particular individual because the immune system of that individual treats the pollen antigens as pathogenic. So more blood flows into our infected area as a result of this vassal dilation process. The increase in diameter of those blood vessels, that brings more blood as well as more wide blood cells. Now, what histamine also does is it increases the permeability of the nearby capillaries to water and that makes those capillaries leaky.