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Dog Coughing Up Green Mucus (Why It Happens)

By Patricia Williams
Last updated: November 14, 2025

When your dog starts coughing up green mucus, it can be alarming — especially when the discharge looks thick, slimy, or colored.

We outline the common reasons why a dog may cough up yellow mucus, what you can do at home, and when it’s time to seek veterinary help.

Table of Contents

Dog Coughing Up Green Mucus: Why It Happens

A dog coughing up green mucus usually indicates an infection or buildup of pus within the airways or lungs. This can be due to respiratory infections like kennel cough, bacterial pneumonia, or sinus infections that drain into the throat. Sometimes, the color change from clear to greenish-yellow means white blood cells are fighting off bacteria — a clear sign of inflammation.

Environmental irritants, allergies, or even foreign material stuck in the airways can also lead to coughing and mucus production.

Green mucus is rarely just from a mild cold — it often points to something your vet should evaluate.

Dog Coughing Up Green Mucus: Common Causes

Respiratory Infections

Respiratory infections are one of the leading causes of dogs coughing up green mucus. Kennel cough, canine influenza, and bacterial bronchitis can all inflame the airways, leading to excess mucus that turns green as immune cells and bacteria mix.

You may notice your dog hacking persistently, producing thick sputum, sneezing, or showing fatigue. The infection can start in the upper airways and move deeper into the lungs if left untreated.

Because green mucus often indicates bacteria are involved, your vet might prescribe antibiotics to clear the infection.

Dogs recovering from viral infections may also develop secondary bacterial infections — a key reason to monitor symptoms closely rather than waiting for them to pass on their own.

Pneumonia

Pneumonia in dogs can develop from untreated infections, aspiration (inhaling food or vomit), or weakened immunity.

It causes inflammation and pus buildup inside the lungs, leading to coughing fits and green mucus that can be tinged with yellow or even blood.

Dogs with pneumonia often breathe rapidly, have nasal discharge, and may lose their appetite. The coughing can be deep and wet-sounding, often worse at night or after exercise.

This is a serious medical condition that needs veterinary treatment, usually involving antibiotics, hydration, and sometimes oxygen therapy.

If your dog’s cough is producing green mucus and they seem tired or refuse food, pneumonia should be high on the list of possible causes.

Sinus or Upper Airway Infection

Sometimes, the problem isn’t in the lungs but higher up — in the nasal passages or sinuses. When the sinuses are infected, thick green mucus can drain down the throat, leading to coughing or gagging as the dog tries to clear it.

You may also see nasal congestion, sneezing, or a runny nose with green or yellow discharge. Dogs with long noses (like Greyhounds or Collies) are more prone to sinus issues due to narrow nasal passages.

If untreated, sinus infections can become chronic, leading to recurring bouts of coughing and mucus buildup. A vet can help by flushing the sinuses and prescribing the right medication to reduce inflammation and bacteria.

Foreign Body in the Airway

Dogs are naturally curious and may inhale small grass pieces, seeds, or dust while sniffing outdoors. When a foreign object lodges in the throat or nasal passages, the body reacts by producing excess mucus to flush it out.

Over time, if bacteria accumulate around the lodged object, the mucus may turn green or yellow.

You might notice your dog coughing suddenly after playing outside, making gagging motions, or pawing at their face. Some dogs may even show signs of distress or difficulty breathing if the obstruction is deeper.

If coughing persists or worsens, a vet visit is essential. They can examine your dog’s throat or nasal passages using a scope to safely remove any lodged material and prevent infection.

Chronic Bronchitis

Chronic bronchitis is an inflammatory condition of the airways that causes ongoing coughing and mucus production. In some dogs, especially small breeds like Poodles or Cocker Spaniels, this condition can become long-term.

When secondary bacteria infect the irritated airways, the mucus may change from clear to green.

The cough tends to sound dry and hacking initially but can become wet and phlegmy as the condition progresses.

Environmental factors like cigarette smoke, dust, or strong cleaning fumes can worsen the irritation. Managing bronchitis involves anti-inflammatory medications, cough suppressants, and lifestyle changes — like avoiding irritants and keeping your dog in a well-ventilated space.

Allergies and Environmental Irritants

Although allergies themselves don’t usually cause green mucus, they can trigger chronic inflammation that makes dogs more prone to secondary infections.

For example, a dog allergic to pollen or household dust might have constant nasal congestion and sneezing. This creates the perfect breeding ground for bacteria, turning clear mucus green over time.

You may also notice watery eyes, itching, or frequent head shaking along with coughing.

Cleaning your dog’s bedding regularly, using air purifiers, and keeping windows closed during high-pollen seasons can help reduce allergic triggers.

What to Do If Your Dog Is Coughing Up Green Mucus

If your dog is coughing up green mucus but otherwise acting normal, monitor closely for any changes in appetite, breathing, or energy levels. Offer plenty of fresh water to keep mucus thin and easier to expel.

Steam therapy — running a hot shower and letting your dog breathe in the warm vapor (without getting wet) — can help loosen congestion.

Avoid exposing your dog to cigarette smoke, perfumes, or aerosol sprays that can worsen airway irritation. Keep your dog warm and indoors during recovery to prevent the infection from spreading or worsening.

If the mucus persists for more than two days, becomes thick or foul-smelling, or your dog starts breathing heavily or refusing food, it’s time to see a vet. Green mucus is rarely harmless and often means there’s an infection that needs medication.

When to Call or Visit Your Vet

You should contact your veterinarian promptly if you notice any of the following signs:

Green or yellow mucus that lasts more than 48 hours.
Coughing accompanied by lethargy, fever, or loss of appetite.
Rapid, shallow, or labored breathing.
Wheezing or crackling sounds in the chest.
Nasal discharge with a foul odor or blood.
Refusal to eat or drink.
Coughing up large amounts of phlegm or vomit.

If your dog’s coughing seems severe or they appear to be struggling to breathe, don’t wait — go to an emergency vet immediately. Early treatment can prevent complications like pneumonia or airway collapse.

Key Takeaway

A dog coughing up green mucus is a clear sign that something more serious than a mild cold is happening. The green color often means infection, inflammation, or pus in the respiratory system — all of which require prompt attention.

While mild cases might improve with rest and home care, most dogs need antibiotics or other veterinary treatments to recover fully.

Monitor your dog’s energy, appetite, and breathing closely, and don’t hesitate to call your vet if things don’t improve within a couple of days.

With early care and proper treatment, most dogs bounce back quickly and breathe easily again — leaving those worrying coughs and green mucus behind.