Illustration showing the acute and late phase allergic reaction in the nasal turbinates, caused by an allergen such as pollen (bottom center) initiating an allergic reaction. Antigenic components from the pollen attach to surface receptors on mast cells (blue, center), which in turn release histamine (pink molecules). The histamine triggers vascular permeability (leaking vessels), leading to mucosal edema. Administration of intranasal steroid sprays can alleviate symptoms in acute phase and late phase allergic reaction.