If your dog is coughing up phlegm, it’s a clear sign that the airways are irritated, inflamed, or struggling to clear something from the respiratory tract.
Phlegm is the body’s way of trapping irritants or infection, so its presence usually means your dog’s respiratory system needs support.
We outline the common causes of a dog coughing up phlegm, what you can do at home, and when to seek veterinary help.
Table of Contents
Dog Coughing Up Phlegm: Why It Happens
A dog coughing up phlegm is typically reacting to airway inflammation, respiratory infections, chronic bronchitis, mucus buildup in the lungs, allergies, or deeper issues affecting the throat or trachea.
Phlegm forms when the body releases mucus to protect and clear the airways, and coughing is the mechanism used to expel it.
While mild coughing can be normal, coughing up phlegm signals that the respiratory system is struggling to stay balanced.
Dog Coughing Up Phlegm: Common Causes
Respiratory Infections
Respiratory infections are among the most frequent causes of dogs coughing up phlegm. These infections irritate both the upper and lower airways, prompting the body to produce mucus that eventually becomes thick, cloudy, or sticky phlegm.
Dogs may cough in deep, repetitive bursts as their lungs or throat try to clear the buildup.
Kennel cough often produces a harsh, honking cough that may bring up light phlegm, while bronchitis and pneumonia create wetter, heavier phlegm that may appear yellow or green.
As inflammation worsens, the airway lining becomes more sensitive, and dogs cough more aggressively, increasing phlegm production.
Left untreated, respiratory infections can progress, leading to fatigue, difficulty breathing, and severe inflammation.
Read more: Dog Coughing Up Phlegm With Blood (When to worry)
Chronic Bronchitis
Chronic bronchitis causes persistent inflammation inside the bronchial tubes, which leads to daily coughing and frequent phlegm production.
The lungs produce thick mucus in response to ongoing irritation, and dogs often cough up phlegm when waking, during excitement, or after exercise.
Over time, the inflammation becomes self-perpetuating. The airway lining thickens, the lungs lose elasticity, and the mucus becomes harder to clear.
Phlegm may vary from foamy white to yellowish if infection develops. Chronic bronchitis is significant because it does not resolve without management and can lead to long-term respiratory decline.
Allergies or Environmental Irritation
Dogs with allergies frequently produce phlegm when exposed to triggers such as pollen, dust, mold, smoke, or strong scents.
When allergens enter the airways, the body responds with inflammation, swelling, and mucus release — all of which contribute to phlegm formation.
Coughing may happen suddenly when the dog encounters the irritant or may continue daily during allergy season. Dogs often sniff continuously outdoors, increasing exposure to environmental allergens that irritate the throat and lungs.
Allergic coughing is important to address because ongoing inflammation makes the airways more sensitive and prone to deeper infections.
Acid Reflux or Throat Irritation
Stomach acid traveling upward into the throat can inflame the tissues, causing a dog to cough and produce phlegm in an attempt to soothe the irritation.
Phlegm may appear frothy, clear, or slightly white. Acid reflux often becomes worse after eating, drinking, or lying down, and dogs may lick their lips, swallow repeatedly, or seem uncomfortable in the throat area.
Repeated reflux episodes cause the throat to produce more mucus, eventually leading to chronic coughing with phlegm.
This condition is important to identify early because untreated acid irritation can make swallowing painful and increase airway sensitivity.
Heart Disease
Heart disease can cause fluid to accumulate in or around the lungs, which triggers coughing and the production of thin, frothy phlegm.
Dogs may cough more at night or after resting, as fluid shifts and irritates the airways. As heart function declines, the cough becomes more frequent and productive.
Phlegm caused by heart issues often indicates that the lungs are struggling to stay clear and that blood flow is becoming compromised.
Dogs may also pant, breathe rapidly, tire easily, or become restless after lying down. This cause is serious because heart-related coughing can progress rapidly.
Foreign Object or Debris in the Airway
If a dog inhales grass, dust, seeds, or small particles, the airway becomes irritated, leading to coughing fits that bring up mucus or phlegm.
Dogs often cough abruptly and repeatedly as their body tries to push out the irritant.
Even after the object moves or dislodges, the throat and airway can remain inflamed, producing ongoing phlegm.
Dogs may paw at their mouth, swallow constantly, or gag. If the object remains trapped deeper in the airway, phlegm coughing persists and may become more severe.
Lung Issues or Airway Tumors
Masses in the lungs or trachea can block airflow, irritate airway tissues, and cause phlegm buildup that the dog coughs up regularly.
Tumors may cause gradual or persistent coughing, unusual breathing sounds, or fatigue. When lung tissue becomes affected, phlegm becomes a chronic symptom as the body tries to clear the obstruction.
This cause is significant because tumor-related coughing tends to worsen over time and may lead to more serious respiratory distress.
Parasites Affecting the Lungs
Lungworms and heartworms can damage lung tissue and create inflammation that leads to phlegm production. As parasites migrate or multiply, the irritation increases, forcing the dog to cough up mucus.
Dogs may also show fatigue, reduced stamina, or sudden coughing episodes that worsen with physical activity.
Parasitic lung issues require treatment as they can progress into severe respiratory problems.
Read more: Dog Coughing and Hacking Suddenly (Sudden respiratory changes)
What to Do If Your Dog Is Dog Coughing Up Phlegm
Begin by keeping your dog calm and restricting activity. Movement and excitement often intensify coughing and make phlegm production worse. Place your dog in a quiet room with clean, fresh air, avoiding smoke, aerosols, cleaning products, or strong scents.
Offer fresh water to soothe the throat and loosen mucus. Observe the color and thickness of the phlegm, as this can provide clues about infection or inflammation. Yellow, green, or foul-smelling phlegm suggests bacterial involvement.
Monitor your dog’s breathing closely. If breathing seems rapid, labored, or noisy, the condition may be more serious. Avoid giving human cough medications, as many ingredients are toxic to dogs and can mask symptoms while leaving the underlying issue untreated.
If phlegm production continues beyond a day or two, worsens, or appears alongside lethargy or fever, your dog needs veterinary evaluation.
When to Call or Visit Your Vet
You should seek veterinary care promptly if your dog is coughing up phlegm and:
• The phlegm is yellow, green, or bloody.
• The coughing is constant, worsening, or painful.
• Breathing becomes fast, shallow, or labored.
• Your dog refuses food or water.
• Fever, lethargy, or nasal discharge appears.
• The cough happens at night or after resting.
• Your dog is a puppy, senior, or has heart or lung issues.
• Coughing lasts more than 24–48 hours without improvement.
Phlegm indicates inflammation or infection that rarely resolves without intervention.
Read more: Dog Coughing Up Mucus (Thick mucus explained)
Key Takeaway
A dog coughing up phlegm is dealing with respiratory irritation, infection, allergies, chronic bronchitis, throat inflammation, or a deeper lung issue.
While occasional coughing is normal, phlegm means the airways are actively responding to something significant.
By monitoring symptoms closely and seeking veterinary care when needed, you can help your dog breathe easier, heal faster, and avoid complications.