Runny Nose in Horses: Types, Causes & Diagnosis

A runny nose in horses can range from a small amount of clear fluid to thick, foul-smelling, or bloody discharge. While an occasional runny nose is not always cause for concern, persistent or unusual discharge can indicate a problem affecting the respiratory tract, sinuses, teeth, or guttural pouches.

The appearance of nasal discharge provides useful clues about its cause. Its color and consistency, odor, and whether it comes from one or both nostrils can all help narrow down where the problem originates. Other symptoms, including fever, coughing, facial swelling, or difficulty breathing, can provide additional information.

Some causes of a runny nose are contagious, making early recognition particularly important in barns where horses have close contact with one another. Other causes require treatment of an underlying problem such as sinus or dental disease.

What Is a Runny Nose in Horses?

A runny nose in horses refers to fluid or other material draining from one or both nostrils. Nasal discharge can vary in color, consistency, smell, and quantity depending on where it originates and what is causing it. ^[1][2]

A runny nose is a symptom rather than a disease itself. The appearance and duration of signs, whether it comes from one or both nostrils, and the presence of other symptoms provide some information about the potential underlying cause. ^[1][2][3]

Evaluating a Runny Nose

The appearance and pattern of nasal discharge can provide useful clues about where it originates and what may be causing it. Veterinarians interpret the characteristics of nasal discharge together with the horse’s other symptoms, medical history, and physical examination findings.

Features of a runny nose that veterinarians use during their assessment include:

• Color
• Consistency
• Odor
• Whether it comes from one or both nostrils
• Presence of blood, pus, feed material, or other components
• When the discharge occurs, such as during eating or after exercise

Changes over time are also important. For example, clear discharge associated with a respiratory infection may become thicker as inflammation and mucus production increase.

Persistent discharge, a foul odor, bleeding, or material coming from only one nostril all warrant veterinary investigation.

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Color

The color of nasal discharge is straightforward for horse owners to monitor, but it should not be interpreted on its own.

Clear discharge is not always harmless, and yellow or green discharge does not automatically confirm a bacterial infection. ^[3]

Table 1. Color of nasal discharge in horses ^[3]

Consistency, Composition & Odor

The consistency and contents of nasal discharge provide additional information about the type of material leaving the respiratory tract. Thin, watery discharge is described as serous, while thicker mucus may be described as mucoid, mucopurulent, or purulent depending on the amount of mucus and pus present. ^[3]

These terms describe appearance rather than a specific diagnosis. For example, purulent discharge indicates the presence of inflammatory material but does not identify where the problem originated or which organism, if any, is involved. ^[3]

Odor also provides useful information about the possible cause. Foul-smelling discharge is particularly concerning when it is persistent and comes from one nostril, as this pattern can occur with sinus disease, dental-related infection, or other conditions that allow infected or damaged material to accumulate. ^[3]

Table 2. Consistency and composition of nasal discharge in horses ^[3]

Origin

Whether discharge comes from one nostril or both can help narrow down where the problem originates. Conditions affecting one nasal passage, one sinus, or an upper cheek tooth on one side are more likely to produce one-sided discharge. Problems involving the broader respiratory tract are more likely to produce discharge from both nostrils. ^[3]

This pattern is a useful indicator, but it doesn’t apply in every case. Material can move through the throat or nasal passages, and disease involving the guttural pouches can produce unilateral or bilateral discharge. Veterinarians interpret the nostril pattern together with other characteristics and the presence of other symptoms. ^[3]

Table 3. Origin of nasal discharge in horses ^[3]

Circumstances

When the discharge appears can provide additional clues about its source. A runny nose that occurs during eating points toward a different problem than discharge that appears only after strenuous exercise.

Feed, saliva, or water coming from the nostrils during or shortly after eating can indicate a swallowing problem or choke. Blood that appears during or after hard exercise may originate from the lower respiratory tract, while bleeding that occurs at rest or without an obvious trigger raises concern for other causes. ^[3]

Table 4. Circumstances associated with runny nose in horses ^[3]

Related Symptoms

Symptoms occurring alongside a runny nose can help narrow down the possible cause. Other symptoms may include: ^{[1][3][4][2][5]}

• Coughing
• Fever
• Reduced appetite
• Lethargy
• Swollen or abscessed lymph nodes around the jaw or throat
• Facial swelling
• Reduced airflow through one nostril
• Noisy breathing
• Difficulty breathing
• Difficulty swallowing
• Feed or water coming from the nostrils

The combination of symptoms informs the diagnosis. Fever and coughing with discharge from both nostrils are more consistent with a respiratory infection, and facial swelling or reduced airflow accompanying persistent discharge from one nostril can occur with sinus disease. ^[1][4][2]

What to Do if a Horse Has a Runny Nose

Owners should monitor a new runny nose closely, especially when the cause is unknown or other symptoms are present. Since contagious respiratory infections can cause nasal discharge, separating an affected horse from other horses is appropriate when infection is suspected. ^[4][5]

Practical steps include: ^[3][4][5]

• Checking the horse’s temperature
• Monitoring the color, consistency, smell, and amount of discharge
• Noting whether discharge comes from one or both nostrils
• Watching for coughing, reduced appetite, lethargy, or swollen lymph nodes
• Separating the horse from others if contagious disease is possible
• Avoiding shared buckets, tack, and grooming equipment
• Contacting a veterinarian if the discharge persists, worsens, or occurs with other symptoms

When to Call the Veterinarian

Symptoms that warrant prompt veterinary attention include: ^[3][5]

• Difficulty breathing or swallowing
• Significant bleeding from the nose
• Feed or water coming from the nostrils

Persistent foul-smelling discharge from one nostril or discharge accompanied by facial swelling also warrants veterinary investigation because sinus or dental disease may be involved. ^[1][2]

Causes of a Runny Nose in Horses

A runny nose in horses can have many causes, ranging from contagious respiratory infections to problems affecting the sinuses, teeth, guttural pouches, and airways. ^[1][3][2]

Respiratory Infections

Contagious respiratory infections commonly cause nasal discharge along with other signs of illness. Equine influenza and equine herpesvirus types 1 and 4 (EHV-1 and EHV-4) are common viral causes of respiratory disease in horses.

Affected horses can develop: ^[3][4][6][7]

• Fever
• Coughing
• Reduced appetite
• Lethargy
• Nasal discharge

EHV-1 and EHV-4 produce very similar respiratory signs, so symptoms alone cannot distinguish between the two infections. Both variants also establish long-term infections in horses and can become active again later, allowing infected horses to shed virus and expose others. ^[7]

Strangles, caused by Streptococcus equi, is another contagious cause of runny nose in horses. Horses typically develop fever and enlargement of the lymph nodes around the jaw or throat. These lymph nodes can form abscesses, and affected horses may also develop: ^[5]

• Thick nasal discharge
• Coughing
• Discomfort when swallowing

Sinus Problems

Sinus disease is one possible cause, particularly when the discharge comes from only one nostril. Fluid and inflammatory material can accumulate within an affected sinus and drain into the nasal passage, resulting in a runny nose. ^[1][2][2]

Sinusitis, or inflammation of the sinuses, is also associated with nasal discharge in horses. Primary sinusitis is inflammation and infection of the sinus itself, often following an upper respiratory tract infection. Secondary sinusitis occurs as a complication of other conditions, such as dental disease, sinus cysts, trauma, or tumors. ^[1][2][3]

Other causes of sinus disease in horses include: ^[1][2][8][9]

• Trauma
• Fungal infection
• Cysts
• Abnormal tissue growth

The discharge is usually thick and may contain pus or blood. Facial swelling, tearing from the eye on the same side, or reduced airflow through that nostril can occur with the nasal discharge, although some horses show little more than a persistent runny nose. ^[1][2][2]

Dental Problems

Dental disease causes a runny nose when infection from an upper cheek tooth enters the sinus beside it. The roots of the caudal upper cheek teeth lie within or against the maxillary sinuses, so infection around a tooth root can breach the thin bone between the tooth socket and the sinus. ^[1][3][8]

The usual result is a secondary sinus infection on that side. Pus drains from the sinus into the nasal passage, producing a persistent, often foul-smelling discharge from one nostril. ^[1][3][2]

Facial swelling or tearing on the affected side can accompany the discharge. Quidding or bit discomfort may be present, but some horses have no obvious problem with eating. ^[1][3]

Guttural Pouch Disease

Disease within a guttural pouch can also cause ongoing nasal discharge. The pouches open into the throat, so material that accumulates inside one or both can drain forward into the nasal passages. ^[3][5][10]

Guttural pouch empyema occurs when pus accumulates inside one or both pouches, often following a bacterial infection such as strangles. The discharge may be one-sided or come from both nostrils, depending on whether one pouch or both are involved. ^[5][10]

Over time, thick material within the guttural pouch forms firm masses called chondroids, which allow infection and discharge to persist. For this reason, veterinarians often consider guttural pouch disease when nasal discharge continues after other signs of strangles have resolved. ^[5][10]

Other Causes

Inflammation of the lower airways contributes to increased respiratory mucus and nasal discharge. Environmental exposure to dust and airborne particles plays an important role in inflammatory airway disease. Some affected horses also show coughing or reduced performance, although nasal discharge does not occur in every case. ^[3][11]

Abnormalities within the nasal passages or sinuses can also produce discharge. Less common causes of runny nose in horses include: ^[1][2][3][2]

• Foreign material lodged in a nasal passage
• Trauma involving the nose or sinuses
• Sinus cysts
• Tumors or other abnormal growths
• Progressive ethmoid hematomas

These conditions often produce persistent discharge from one nostril, though the character of the discharge varies. ^[1][2][2]

Persistent, foul-smelling, bloody, or one-sided nasal discharge warrants veterinary investigation because it raises greater concern for a localized problem within the nasal passages, sinuses, teeth, or guttural pouches. ^[1][2][10]

Diagnosis

When investigating causes of an equine runny nose, veterinarians first consider the appearance of the discharge and any accompanying symptoms. Important clues include whether the discharge comes from one or both nostrils, whether it is clear or thick, and whether the horse also has: ^[1][3][8]

• Fever
• Coughing
• Facial swelling
• Swollen lymph nodes
• Difficulty breathing

The horse’s medical history also narrows down the possible causes. A veterinarian may ask about: ^[1][3][5]

• Recent respiratory illness
• Travel
• Contact with other horses
• Vaccination history
• Dental problems
• How long the discharge has been present

The findings from this initial examination determine which diagnostic tests are most appropriate. ^[1][3][5]

Depending on the suspected cause, diagnostic tests may include: ^{[1][3][5][8][9]}

• Endoscopy
• X-rays
• Ultrasound
• CT scans
• Blood tests
• Nasal or airway samples
• Bacterial culture
• PCR testing

Endoscopy allows the veterinarian to examine the nasal passages, throat, and openings of the guttural pouches and sinuses. It can help identify accumulated discharge, inflammation, masses, bleeding, or material draining from a particular sinus or guttural pouch. ^{[1][3][8][10]}

X-rays and CT scans provide more information about structures that veterinarians cannot fully examine with an endoscope. X-rays reveal changes within the sinuses, teeth, and surrounding bones, while CT produces detailed cross-sectional images of individual sinus compartments and the nasal passages. ^[1][8][9]

Ultrasound complements these tests by helping veterinarians assess structures that lie close enough to the body surface for imaging. Depending on the horse’s symptoms, ultrasound can provide additional information about fluid accumulation, soft tissues, or other abnormalities associated with respiratory disease. ^[3]

When an infectious respiratory disease is possible, veterinarians often collect nasal, nasopharyngeal, or other airway samples. PCR testing can detect genetic material from specific infectious agents, and bacterial culture identifies bacteria present in a sample and guides treatment when bacterial infection is suspected.  ^[4][5][6][7]

Some horses require more than one test because several respiratory disorders produce similar signs. ^[8][9]

Treatment

Treatment depends on the underlying cause. Viral respiratory infections such as uncomplicated equine influenza are generally managed with rest and supportive care, and may require antibiotics depending on the cause and clinical presentation. ^[3][4]

Treatment for strangles varies according to the stage and severity of infection and whether complications are present. ^[5]

Persistent sinus infections may require flushing of the affected sinuses, and some cases require surgery to remove accumulated material or correct the underlying problem. ^[1][2] When dental disease is responsible for a horse’s runny nose, veterinarians treat the affected tooth to address the source of the sinus infection. ^[1]

Guttural pouch infections may require flushing and removal of accumulated material, with additional treatment depending on the cause and severity. ^[5][10]

Management for airway inflammation focuses on reducing exposure to dust and other airborne irritants, with medications used when appropriate to control inflammation or airway narrowing. ^[11]

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Preventing Nasal Discharge in Horses

Not every cause of nasal discharge can be prevented, but appropriate vaccination, biosecurity, respiratory management, and dental care can reduce the risk of several common causes. ^{[1][4][5][11]}

Preventive measures include: ^{[1][4][5][11]}

• Keeping vaccinations current and appropriate for the horse’s risk and exposure
• Isolating new arrivals and horses showing symptoms of respiratory disease
• Avoiding shared water buckets, feed containers, grooming equipment, and tack during disease outbreaks
• Maintaining good ventilation in barns and stables
• Reducing exposure to dust and ammonia from hay and bedding
• Providing regular dental care
• Monitoring horses closely after travel or contact with unfamiliar horses

Vaccination cannot prevent every case of infectious respiratory disease, so it should be combined with appropriate biosecurity. ^[4][5]

Reducing airborne dust and improving ventilation can also help limit respiratory irritation and inflammation. ^[11]

Frequently Asked Questions

Here are some frequently asked questions about runny noses in horses:

Summary

A runny nose in horses can result from respiratory infections, sinus or dental disease, guttural pouch disorders, airway inflammation, or problems within the nasal passages. The appearance and location of the discharge, together with other clinical signs, help guide diagnosis and treatment.

• Clear, green, pus, or bloody discharge can provide important clues about the underlying condition
• Persistent one-sided discharge can indicate a localized sinus, dental, guttural pouch, or nasal problem
• Fever, coughing, facial swelling, difficulty breathing or swallowing, and feed or water from the nostrils warrant veterinary attention
• Diagnostic testing may include endoscopy, imaging, bloodwork, airway sampling, bacterial culture, or PCR testing
• Treatment depends on the cause and may involve supportive care, antibiotics, dental treatment, surgery, or environmental management