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Causes

The causes of allergic rhinitis may differ depending on whether the symptoms are seasonal, perennial, or sporadic/episodic. Some patients are sensitive to multiple allergens and can have perennial allergic rhinitis with seasonal exacerbations. While food allergy can cause rhinitis, particularly in children, it is rarely a cause of allergic rhinitis in the absence of gastrointestinal or skin symptoms.

• Seasonal allergic rhinitis is commonly caused by allergy to seasonal pollens and outdoor molds.
• • Pollens (tree, grass, and weed)

     

    • Tree pollens, which vary by geographic location, are typically present in high counts during the spring, although some species produce their pollens in the fall. Common tree families associated with allergic rhinitis include birch, oak, maple, cedar, olive, and elm.

       

    • Grass pollens also vary by geographic location. Most of the common grass species are associated with allergic rhinitis, including Kentucky bluegrass, orchard, redtop, timothy, vernal, meadow fescue, Bermuda, and perennial rye. A number of these grasses are cross-reactive, meaning that they have similar antigenic structures (ie, proteins recognized by specific IgE in allergic sensitization). Consequently, a person who is allergic to one species is also likely to be sensitive to a number of other species. The grass pollens are most prominent from the late spring through the fall but can be present year-round in warmer climates.

       

    • Weed pollens also vary geographically. Many of the weeds, such as short ragweed, which is a common cause of allergic rhinitis in much of the United States, are most prominent in the late summer and fall. Other weed pollens are present year-round, particularly in warmer climates. Common weeds associated with allergic rhinitis include short ragweed, western ragweed, pigweed, sage, mugwort, yellow dock, sheep sorrel, English plantain, lamb's quarters, and Russian thistle.

     

  • Outdoor molds

     

    • Atmospheric conditions can affect the growth and dispersion of a number of molds; therefore, their airborne prevalence may vary depending on climate and season.

       

    • For example, Alternaria and Cladosporium are particularly prevalent in the dry and windy conditions of the Great Plains states, where they grow on grasses and grains. Their dispersion often peaks on sunny afternoons. They are virtually absent when snow is on the ground in winter, and they peak in the summer months and early fall.

       

    • Aspergillus and Penicillium can be found both outdoors and indoors (particularly in humid households), with variable growth depending on the season or climate. Their spores can also be dispersed in dry conditions.

     

   

• Perennial allergic rhinitis is typically caused by allergens within the home but can also be caused by outdoor allergens that are present year-round. In warmer climates, grass pollens can be present throughout the year. In some climates, individuals may be symptomatic due to trees and grasses in the warmer months and molds and weeds in the winter.
• • House dust mites

     

    • In the United States, 2 major house dust mite species are associated with allergic rhinitis. These are Dermatophagoides farinae and Dermatophagoides pteronyssinus.

       

    • These mites feed on organic material in households, particularly the skin that is shed from humans and pets. They can be found in carpets, upholstered furniture, pillows, mattresses, comforters, and stuffed toys.

       

    • While they thrive in warmer temperatures and high humidity, they can be found year-round in many households. On the other hand, dust mites are rare in arid climates.

     

  • Pets

     

    • Allergy to indoor pets is a common cause of perennial allergic rhinitis.

       

    • Cat and dog allergies are encountered most commonly in allergy practice, although allergy has been reported to occur with most of the furry animals and birds that are kept as indoor pets.

     

  • Cockroaches: While cockroach allergy is most frequently considered a cause of asthma, particularly in the inner city, it can also cause perennial allergic rhinitis in infested households.

     

  • Rodents: Rodent infestation may be associated with allergic sensitization.

     

   

• Sporadic allergic rhinitis, intermittent brief episodes of allergic rhinitis, is caused by intermittent exposure to an allergen. Often, this is due to pets or animals to which a person is not usually exposed. Sporadic allergic rhinitis can also be due to pollens, molds, or indoor allergens to which a person is not usually exposed. While allergy to specific foods can cause rhinitis, an individual affected by food allergy also usually has some combination of gastrointestinal, skin, and lung involvement. In this situation, the history findings usually suggest an association with a particular food. Watery rhinorrhea occurring shortly after eating may be vasomotor (and not allergic) in nature, mediated via the vagus nerve. This often is called gustatory rhinitis.

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• Occupational allergic rhinitis, which is caused by exposure to allergens in the workplace, can be sporadic, seasonal, or perennial. People who work near animals (eg, veterinarians, laboratory researchers, farm workers) might have episodic symptoms when exposed to certain animals, daily symptoms while at the workplace, or even continual symptoms (which can persist in the evenings and weekends with severe sensitivity due to persistent late-phase inflammation). Some workers who may have seasonal symptoms include farmers, agricultural workers (exposure to pollens, animals, mold spores, and grains), and other outdoor workers. Other significant occupational allergens that may cause allergic rhinitis include wood dust, latex (due to inhalation of powder from gloves), acid anhydrides, glues, and psyllium (eg, nursing home workers who administer it as medication).