Dog Coughing Up Phlegm (What It Means and When To Worry )

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 and Hacking Suddenly (Sudden respiratory changes)

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.

Related: Dog throwing up and coughing (Causes explained)

Dog coughing up phlegm but acting normal

A dog may cough up phlegm yet seem otherwise normal if the irritation is mild or early in development. Causes can include allergies, environmental irritants, kennel cough, or minor respiratory inflammation.

Even if energy and appetite are unaffected, persistent coughing with mucus is not normal and can worsen over time.

If coughing lasts more than a few days or becomes more frequent, veterinary assessment is recommended.

Senior dog coughing up phlegm

When a senior dog coughs up phlegm, it often indicates chronic airway or heart-related conditions. Common causes include chronic bronchitis, collapsing trachea, heart disease, respiratory infections, or age-related weakening of the immune

system. Mucus buildup is more common in older dogs and may worsen with lying down or activity.

Because seniors are more vulnerable to complications, ongoing phlegmy coughing should always be evaluated by a veterinarian.

Dog coughing up phlegm at night

Coughing that produces phlegm and worsens at night often occurs because mucus pools in the airways when the dog is lying down.

This pattern is commonly associated with heart disease, bronchitis, or post-nasal drip.

Nighttime coughing should be taken seriously, especially in small breeds or older dogs, as it may indicate progressing heart or respiratory disease.

Dog coughing up phlegm and blood

Coughing up phlegm mixed with blood is a serious warning sign. It may result from severe infection, lung injury, trauma, tumors, blood clotting disorders, or advanced heart disease.

Even small amounts of blood should never be ignored. Immediate veterinary care is essential, as this symptom can indicate a life-threatening condition.

Read more: Dog Coughing Up Phlegm With Blood (When to worry)

Dog coughing up phlegm in the morning

Morning phlegmy coughing often happens because mucus accumulates overnight while the dog is lying down. When the dog gets up and starts moving, the mucus shifts and triggers coughing.

Common causes include post-nasal drip, allergies, chronic bronchitis, or early heart disease—especially in older or small-breed dogs.

If morning coughing becomes frequent or progressively worse, it should be medically evaluated.

Dog coughing up phlegm when excited

Coughing with phlegm during excitement is commonly linked to airway sensitivity, such as a collapsing trachea, kennel cough, or chronic respiratory irritation.

Excitement increases breathing rate and airway pressure, which can dislodge mucus and trigger coughing.

This is especially common in small breeds and senior dogs. Repeated excitement-triggered coughing is not normal and should be assessed to prevent airway damage.

Dog coughing up phlegm after drinking water

When a dog coughs up phlegm after drinking water, it usually means fluid or mucus is irritating the throat or airway. This can happen if the dog drinks too quickly and inhales a small amount of water, triggering a cough to clear the airway.

It may also point to underlying issues such as throat irritation, tracheal sensitivity, collapsing trachea, laryngeal dysfunction, or excess mucus from allergies or respiratory disease.

While an occasional cough after drinking can be normal, repeated or worsening episodes—especially in senior dogs or small breeds—should be evaluated by a veterinarian to rule out airway or heart-related conditions.

Related: Dog coughing white foamy mucus (Why it happens)

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.