Allergic Rhinosinusitis / Allergic Rhinoconjunctivitis


The inflammation of nasal and sinus passages (rhinitis and sinusitis respectively) and/or conjunctiva (conjunctivitis) of the eye in response to an antigen that is inhaled, transported to the site, and deposited on the surfaces of those membranes.

Clinical Signs

May observe any of the following:

  • Sneezing
  • Nasal rubbing
  • Porphyrin secretions may or may not present
  • Swelling of nasal mucous membranes


Allergic rhinitis, sinusitis and rhinoconjunctivitis is a complex of signs that results from an IgE (immunoglobulin type E) antibody reaction to a presenting antigen.

Typically, the body’s immune system responds to foreign substances by producing proteins called antibodies (e.g., IgE). These antibodies bind to antigens (molecules), identified on the foreign substance. The reaction caused by the binding of antibody to antigen is what helps to protect the body from infection. However, when substances believed to be normal, and harmless, trigger a reaction the condition is called an allergy or an allergic response.

When antigen and antibody (IgE) bind in allergic response mast cells which line both nasal passages and eyelids release granules containing a major chemical mediator of the inflammatory response called histamine. The action of histamine on neighboring tissue cells along with other chemical mediators such as eosinophils, prostaglandins, and leukotrienes result in fluid leakage causing swelling of the nasal / sinus / eustachian tube passages and conjunctival swelling, irritation, itching, sneezing, and porphyrin tearing in the rat.

Some substances found to cause an allergic response in some rats are:

  • Bedding or litters that produce dust.
  • Owners that smoke around the rat’s environment.
  • The use of cage cleaning products around rats or the cage insufficiently rinsed and dried following the use of cleaning product.
  • The use of perfumed detergents or rinse softeners in bedding.
  • Body perfumes, lotions or perfumed hair products used by pet owner.
  • Exposure to drafts during windy, high pollen seasons.

The condition affects primarily the upper respiratory tract and/or conjunctiva of the eye, and tends to resolve quickly when the offending substance is removed from the environment. However, because this type of allergic response can increase the production of mucus from mucous membranes it can set up an environment for the proliferation of any bacteria that may be residing in the respiratory tract leading to a bacterial infection.

It is important to be aware that respiratory allergies are not overly common in the rat; hence it is wise to have your pet rat assessed by a veterinarian so that a correct diagnosis can be made, and appropriate treatment can be initiated.

For information on rhinitis / sinusitis in acute and chronic respiratory disease caused by infectious agents see articles in sections on Bacteria, Viruses, and Lower Respiratory in the Health Guide section of Rat Guide.


History of disappearance of symptoms when offending substance or substances removed.

Responsive to antihistamines

Presence of esinophils in nasal exudate

Radiograph, if elected, appears normal

*Note: nasal mucosa edema, vasodilation, glandular hyperplasia, and eosinophil infiltration are observed in the lamina propria of rats with allergic rhinitis.


Clinical signs may be alleviated by trying to identify and remove irritant

Rats are obligate nose breathers so where symptoms become bothersome causing the rat breathing difficulty, and the irritant is difficult to determine, it may become necessary for the veterinarian to select from the following treatment options:

Antihistamines (listed) block the histamine receptors on nasal tissue decreasing the effect of histamine release by mast cells.

  • diphenhydramine (Benadryl and generics)
  • chlorpheniramine (Chlor-trimeton and generics)
  • Loratidine (Children’s Claritin)

Because these agents can cause drying of nasal passages it is advised to limit antihistamine use to three or four days.


  • Children’s Sudafed or Children’s Sudafed PE helps by constricting blood vessels to counteract the effects of histamine.

Nonsteroidal Anti-inflammatory Drugs

  • Metacam for reducing inflammation


  • Prednisone or Prednisolone, steroids that help reduce inflammation and are available by prescription.

Additional Treatments

  • Humidified air to help moisten inspiratory air.
  • Nebulizing with normal saline to aid in reducing inflamed tissue and thin secretions.
  • Air purifiers may be helpful in areas where allergens are most prevalent.

For care and treatment of eyes see Conjunctivitis in the Health Guide section of Rat Guide.

For information pertaining to medications refer to the Rat Medication Guide.

Nursing Care

  • Ensure nares and eyes are clean and free of secretions
  • Encourage drinking by offering extra fluid or extra fluid in foods (e.g., juicy types of fruit) to aid in thinning mucus secretion.
  • When choosing to humidify air:
    • Provide humidification with a humidifier, or stay with rat in a closed misted bathroom for 10-to-15-minute intervals, to soothe inflamed irritated breathing passages, and loosen secretions.
    • *Note: cool mist humidifiers or vaporizers may be of more comfort to the rat than steam or heated mist if there is congestion with increased mucus production and swelling of airways.
    • It is important to remember to clean humidifiers or vaporizers following each use to prevent growth of organisms from standing water.

  • When choosing to use a nebulizer:
  • In the event condition does not resolve quickly or condition worsens contact veterinarian to assess for bacterial infection and more appropriate treatment.
  • Outcome

    • Airway remains clear
    • Hydration adequate
    • Nutrition level adequate
    • Clinical signs resolve upon removal of offending substance
    • Clinical signs resolve in response to treatment


    • Avoid known allergens (e.g., perfumed or fragranced detergents and softeners, pine, cedar or dusty litter, harsh cage detergents, smoking in or around rats).
    • Locate cage or housing in draft free area.
    • Rinse cage(s) well following use of disinfectants or cleaning solutions. For appropriate cleaning solutions see:
    • Use hypoallergenic, fragrance-free detergents when washing material bedding and rinse well. Avoid softeners when washing or drying.
    1. Jeon, S., Kim, J., Kim, E., Ahn, S., & Kim, B. (2005). Rat model of platelet-activating factor-induced rhinosinusitis. Ann Otol Rhinol Laryngol, 1114(5), 393-8.
    2. Oglesbee, B. L. (2011). Blackwell’s Five-Minute Veterinary Consult: Small Mammal (2nd ed.). Chichester, West Sussex: Wiley-Blackwell.
    3. Sugimoto, Y., Kawamoto, E., Chen, Z., & Kamei, C. (2000). A new model of allergic rhinitis in rats by topical sensitization and evaluation of H1-receptor antagonists. Immunopharmacology, 48(1), 1-7.


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