Blame it on your mast cells. Mast cells are the cells that start off your allergic reaction.

The problem is the location of these cells. They cluster around the respiratory tract, mouth, feet, internal body surfaces (like the digestive tract) and your blood vessels. Your eyes also have mast cells.  All of these surfaces will protect themselves with inflammation when injury occurs.

The mast cells in all these locations release histamine. Histamine is the culprit behind itching, redness and tearing as well as sneezing and your runny nose. In the case where an allergic reaction affects the whole body, the reaction moves from the site of the initial exposure to the other mast cells in the body.

Histamine actually performs a number of important functions in your body. It’s not just an annoyance! In fact, histamine has a role in your sleep cycle.  It also helps to regulate some of your digestive tract and acts as a neurotransmitter. It’s even an important factor in sexual response. Histamine is released by mast cells in the genitals as part of an orgasm. So, histamine isn’t the problem; it’s too much histamine.

Let’s get back to the runny nose and teary eyes. The presence of an airborne allergen in your nose and eyes will result in inflammation in your sinuses and eye membranes. That’s histamine overload. You’ll generally experience this reaction in your nose as congestion and in your eyes as irritation and redness.

However, with your nose the swelling of the lining will then cause fluid to be pressed out of the small blood vessels in your nasal passages. The combination of this excess fluid and the normal mucus in your nose causes the runny nose.