The immune system fights off harmful foreign substances like bacteria and viruses by making antibodies to them. Each antibody recognizes and binds to one specific foreign substance – like a key fitting into a lock. Millions of different antibodies circulate in your bloodstream and are present throughout the body to help fend off any unwanted substances.

The antibodies usually involved in allergic rhinitis are called immunoglobulin E (IgE). IgE binds to receptors located on certain cells in the nasal lining called "mast cells." These cells have granules that contain a chemical called "histamine." When an allergen binds to IgE on mast cells, they release histamine. The released histamine latches onto nearby small blood vessels, causing them to dilate (widen). This results in swelling, redness and inflammation, and leads to unpleasant symptoms such as an itchy, stuffy or runny nose.

Each allergen produces a distinct set of IgE antibodies. These distinct antibodies are responsible for various allergies. The quantity of IgE antibodies present determines the severity of the allergic reaction. The more IgE antibodies there are to a specific substance, the more pronounced the reaction will be.