The signs and symptoms are familiar to many:
- Sneezing often accompanied by a runny or clogged nose
- Coughing and postnasal drip
- Itching eyes, nose, and throat
- Allergic shiners (dark circles under the eyes caused by increased blood flow near the sinuses)
- The "allergic salute" (in a child, persistent upward rubbing of the nose that causes a crease mark on the nose)
- Watering eyes
- Conjunctivitis (an inflammation of the membrane that lines the eyelids, causing red-rimmed, swollen eyes, and crusting of the eyelids).
As soon as the allergen lands on the mucous membranes lining the inside of
the nose, a chain reaction occurs that leads the mast cells in these tissues to
release histamine and other chemicals. These powerful chemicals contract certain
cells that line some small blood vessels in the nose. This allows fluids to
escape, which causes the nasal passages to swell, resulting in nasal congestion.
Some of the above information has been provided with the kind permission of the National Institutes of Health (www.nih.gov)