Rhinitis, an inflammation of the mucous membranes in the nose, is typically caused by common colds and other viral conditions. Allergic rhinitis (or hay fever), which is the most common form of rhinitis, causes irritation of the nasal membranes due to different airborne allergens (usually outdoor or indoor).

Seasonal hay fever

 Seasonal hay fever (or "seasonal allergic rhinitis) is caused by outdoor allergens and usually affects people from spring through fall, depending on the time of year that certain plants and trees release pollen into the air. Allergens for seasonal hay fever include:

  • Tree pollen (in the spring)
  • Grass pollen (in the late spring and summer)
  • Weed pollen (in the fall)
  • Fungi and mold spores (in the warmer parts of the year)

Perennial hay fever 

Perennial hay fever (or "perennial allergic rhinitis") is caused by allergens other than pollen, usually those found in the home. These include:

  • Animal dander. Cats in particular are the cause of allergic rhinitis for many people because they frequently lick their coats, releasing dander and inflammatory proteins from their saliva into the air. Unlike dogs, cats tend to closely share living spaces with their owners and houseguests.
  • Indoor mold. An allergy to mold that grows in damp, dark areas of a home. A kitchen can be especially problematic for rhinitis sufferers, who are more likely to have both outdoor and indoor allergens affect them.
  • Dust mites
  • Cockroaches

Once triggered by any of these allergens, the allergic reaction is caused by the release of histamine and other substances that result in swelling of nasal and eye tissues, the secretion of mucous, and, possibly, the constriction of airways.