SYMPTOM
Nasal discharge
Visible discharge from one or both nostrils that may be clear, cloudy, yellowish, greenish, or occasionally blood-tinged.
Upper Respiratory Infection
Nasal discharge is one of the cardinal signs of upper respiratory infection in cats and dogs. In cats, feline herpesvirus-1 and calicivirus are the most common viral causes, while Bordetella bronchiseptica and Chlamydophila felis are bacterial agents that may produce nasal discharge. In dogs, canine infectious respiratory disease complex (kennel cough) involving parainfluenza, Bordetella, and other organisms commonly produces nasal discharge alongside coughing.
Chronic Rhinosinusitis
Persistent nasal discharge may reflect chronic inflammation of the nasal passages and sinuses. In cats, this frequently develops as a sequel to acute viral infection, with damage to the mucociliary apparatus allowing secondary bacterial colonisation. In dogs, chronic rhinitis may be associated with aspergillosis, lymphoplasmacytic rhinitis, or other inflammatory processes. The character of the discharge — serous, mucoid, or mucopurulent — provides clues about the nature of the underlying inflammation.
Nasal Foreign Body
Foreign material lodged in the nasal passage typically produces acute onset, unilateral nasal discharge that may be mucoid or mucopurulent and is often accompanied by intense sneezing. The discharge tends to be persistent and may become progressively more purulent as secondary bacterial infection develops around the foreign material.
Dental Disease
Advanced dental disease involving the upper teeth can create oronasal fistulae, allowing oral contents to enter the nasal passage and producing chronic unilateral nasal discharge. The discharge in dental-associated nasal disease may be mucopurulent and is often accompanied by sneezing, particularly after eating or drinking.
Nasal Neoplasia
Tumours within the nasal passages can produce nasal discharge that may be serous, mucopurulent, or haemorrhagic depending on the tumour type and extent. Nasal lymphoma in cats and adenocarcinoma in dogs are among the more commonly encountered nasal tumours. The discharge from nasal tumours tends to be progressive, often beginning unilaterally before potentially becoming bilateral as the tumour extends.
Allergic Rhinitis
Sensitivity to inhaled allergens can produce clear, serous nasal discharge alongside sneezing. Allergic rhinitis may follow seasonal patterns corresponding to pollen exposure or may be perennial if triggered by indoor allergens such as dust mites. The discharge is typically bilateral, clear, and non-purulent, distinguishing it from infectious causes.
Why timing matters
Early observation
Early nasal discharge may present as a slight moistness around the nostrils or mild clear discharge that is easily overlooked, particularly in animals that groom frequently. The discharge may be intermittent, most noticeable after resting or sleeping when secretions have accumulated. At this stage, the animal may otherwise appear well and the discharge may be attributed to minor environmental irritation.
Later presentation
As the underlying cause progresses, nasal discharge may become more persistent, increase in volume, and change character from clear and serous to cloudy, yellowish, greenish, or blood-tinged. Persistent discharge may cause crusting and excoriation around the nostrils, and the animal may show signs of nasal obstruction such as mouth breathing, snoring, or reduced appetite due to impaired olfaction. The fur around the nostrils and on the forepaws (from face-rubbing) may become stained and matted.
The trajectory of nasal discharge depends on its cause. Acute viral infections typically produce discharge that progresses from serous to mucopurulent over several days before resolving within one to three weeks. Chronic rhinosinusitis produces discharge that persists or recurs over months to years, often waxing and waning in severity. Foreign body-associated discharge tends to persist without resolution until the foreign material is removed. Neoplastic causes typically produce progressively worsening discharge that may transition from mucoid to haemorrhagic as the tumour grows.
Conditions commonly associated
Chronic Upper Respiratory Disease in Cats
Nasal discharge is a cardinal feature of chronic upper respiratory disease in cats, ranging from clear and serous during early or mild episodes to mucopurulent with established secondary bacterial infection and turbinate damage.
Kennel Cough in Dogs
Nasal discharge in kennel cough typically begins as clear and watery, reflecting upper airway inflammation, but may become thicker and mucopurulent if secondary bacterial infection develops.
Nasopharyngeal Polyps
Nasal discharge may develop with nasopharyngeal polyps, particularly if secondary infection occurs.
Pneumonia
Respiratory infection often produces discharge that drains from the nose.
Pneumonia
Thick or discoloured nasal discharge may accompany respiratory infection.
Feline Herpesvirus (FHV-1)
Inflammation of nasal passages produces discharge that may become purulent with secondary infection.
When to explore further
Nasal discharge that persists for more than two to three weeks without resolution, or that recurs in a recurring pattern, may suggest a chronic underlying process rather than a self-limiting acute infection.
Unilateral nasal discharge — consistently from only one nostril — may suggest a localised cause such as a foreign body, dental fistula, or mass lesion on the affected side, which carries different implications from bilateral discharge.
Discharge that is blood-tinged or frank epistaxis (nosebleed), particularly if recurring, may suggest mucosal erosion, turbinate destruction, or a vascular or neoplastic process within the nasal passages.
A change in discharge character from clear and serous to thick, coloured, or malodorous may indicate secondary bacterial infection or progression of the underlying disease process.
Nasal discharge accompanied by facial deformity, asymmetric swelling over the nasal bridge, or displacement of the eye may suggest an expansile process within the nasal cavity or sinuses.
Observing whether the nasal discharge is consistently from one nostril or both, its character (clear, cloudy, coloured, blood-tinged), and whether it varies with time of day, activity level, or environmental conditions can help characterise the underlying process. Noting any associated signs such as sneezing, changes in breathing sounds, reduced appetite, or facial swelling provides additional context. Photographing the discharge and any visible nasal changes at regular intervals can create a useful visual record for tracking progression.
Last reviewed: 24 April 2026 · Dr Alastair Greenway MRCVS