Why Is My Dog Coughing Up Phlegm? 10 Common Reasons

Dogs have much weaker immune systems than some other household pets.

So, as a dog owner, you should always look out for unusual symptoms in their behaviors to seek medical treatments immediately.

If your dog is much less active than usual and spits out phlegm, something is definitely going on! Why is my dog coughing up phlegm? 

My article will compile the most likely culprits behind the issue. Keep scrolling!

Why Is My Dog Coughing Up Phlegm?

why is my dog coughing up phlegm

Your dogs might have been triggered by allergens, stuck foreign objects, or mild illness like Kennel Cough, flu, and sore throats.

But if the coughs and wheezes worsen over time, you should consider the possibility of serious, deadly diseases like lung cancer, tracheal collapse, or pneumonia.

Canine Influenza

Commonly referred to as flu, influenza is one of the most common and contagious diseases your canine friend might encounter.

The H3N2 and H3N8 viruses cause a lot of severe flu symptoms (aside from your dog coughing phlegm), such as:

  • Sneezing
  • Fever
  • Nasal discharge
  • Lethargy
  • Pneumonia (which might be deadly if your dog has a weak immune system)

Canine influenza often results from your dog’s close interactions with other sick dogs – usually at dog parks, grooming facilities, kennels, or dog shelters.

Consult professionals immediately if you suspect your dog is infected, and sign up for vaccinations/isolation treatments recommended by experts and vets.

Environmental Allergens

Are there any strong environmental allergens in the dog’s living environment that might trigger unwanted reactions? Cases in point are: 

  • Mold spores
  • Pollent
  • Dust mites
  • Plants


Too much exposure to those substances will lead to the dog coughing up phlegm, usually as a result of at least one of the following scenarios: 

  • The allergens irritate the dog’s respiratory passage
  • The dog’s inflammatory responses are triggered, increasing mucus and phlegm buildup.
  • The dog coughs out as an instinctual reflex to get rid of mucus and itchy particles in its respiratory system.

Other allergy symptoms are nasal discharge, sneezing, wheezing, and even breathing difficulty in worse cases.

Stuck Foreign Objects

Another common reason behind your dog hacking up phlegm is foreign objects (e.g., small items, toys, food) stuck in the dog’s airway or throat.

As his sensitive issues are triggered, the dog will try to expel the objects through constant coughing.

These irritations also stimulate faster mucus production to help protect and lubricate the airway, which explains the phlegm.

Needless to say, this situation is extremely dangerous; imagine what it would be like for you if your entire breathing airway is obstructed! 

Seek emergency veterinary care right away to address the issue properly, and do not try to solve it yourself if you lack both experience and necessary skills.

Tracheal Collapse

Tracheal Collapse

Tracheal collapses, while also appearing in some other animals, are mostly common among dogs, especially smaller ones with weak immune systems.

As the name suggests, it weakens and narrows the trachea (the tub carrying air to the dog’s lungs from its mouth and nose), resulting in major collapses and numerous respiratory issues.

A dog with tracheal issues will cough out phlegm, let out wheezing/honking sounds and rapid breathing, and cannot do physical exercise as well as it usually does.

Worse, fainting episodes might even occur during physical activity or excitement!

But here’s the great news: this chronic condition can be handled with proper treatment and care.

Make sure you look out for your dogs constantly (to detect unusual symptoms as early as possible) and consult experienced, licensed veterinarians for the best solutions.

Heart Diseases

Dogs are just as (if not even more) vulnerable to heart diseases as us humans. These conditions range from chronic illnesses to congenital diseases from birth, including:

  • CHF (Congestive Heart Failure): The heart cannot pump blood properly, causing severe fluid accumulations in the dog’s tissues and lungs.
  • Valvular Heart Diseases: Popular among senior, aging dogs, they involve severe issues with the mitral/heart valves, weakening the heartbeats and leading to blood regurgitation.
  • DCM (Dilated Cardiomyopathy): Dogs with DCM suffer from enlarged/weakened heart muscles, failing to maintain efficient blood pumps.
  • Hypertrophic Cardiomyopathy: This condition involves thickened heart muscles and slower blood circulation. While it is more popular in cats, some dogs with weak systems might also encounter hypertrophic cardiomyopathy.
  • Congenital Defects: Your dog might have been born with severe structural abnormalities (e.g., septal defects or PDA/patent ductus arteriosus), which impacts normal heart functions and causes him to cough out phlegm.
  • Arrhythmias: Violent, wet coughs also likely stem from arrhythmias or abnormal heart rhythms.

Some of these conditions are not exactly curable (especially if detected too late).

Still, experts and vets can help you and your dog manage them via lifestyle adjustments, dietary changes, and medications.

Regular checkups are also important if you want to mitigate the damage and address the conditions from the early stages.


Pneumonia, usually caused by irritants that intrude on the dog’s lower respiratory tracts, is very common among aging and senior dogs.

Infectious agents (parasitic, fungal, viral, and bacterial organisms) have been the most common culprits behind pneumonia.

But sometimes, even inhaling foreign objects (as discussed in the above section) also causes aspiration pneumonia; look out for them if your dog has serious neurological issues or compromised gag reflexes!

Treatments and diagnosis vary depending on the root cause.

But overall, they usually involve antifungal medications (to handle fungal infections), antibiotics (for serious bacterial infections), and extra support through fluids and oxygen therapy.

Kennel Cough

Why is my dog coughing up white foamy phlegm? Observe how your dog coughs; are the coughs dry and persistently hacking? 

Then, he might have gone down with Kennel Cough, a common respiratory infection often found in places with dense dog populations like grooming facilities, dog parks, and kennels (hence the name).

Most of the time, Kennel Coughs are quite mild and can resolve themselves over time.

Rumor has it that Lysol can kill Kennel Cough, but that’s just an old wives’ tale, and you should never apply this to your pooch.

But if your dog spits out phlegm, the situation has become much more serious; bring him to a vet to get cough suppressants, antibiotics, and other similar treatments.

Lung Problems

Lung problems are quite hard to detect and usually encompass some of the issues mentioned above (e.g., asthma, pneumonia, etc.)

Common symptoms include heavy coughing, wheezing, labored breathing, and higher respiratory rates.

If you realize more than one of these symptoms in your dog, note them down and schedule a medical appointment immediately.

Sore Throats

When your dog coughs up phlegm, sore throats are another likely possibility. Anything can cause it: irritants, allergies, viral infections, and even excessive barking.

Observe whether your canine friend has trouble swallowing, coughs out phlegm, barks hoarsely, or drools too much; they are the clear indicators that you must seek appropriate treatments and pain relief for his throat as soon as possible.


And here we come to the worst-case scenario – cited as the most common reason behind the deaths of older dogs.

But do not lose hope: surgery, palliative care, radiation therapy, chemotherapy, etc., can still reduce its effects or extend your dog’s lifespan to a certain extent.

And if you want to detect cancer before it is too late, then regular check-ups and diagnoses are a must.

When Should I Bring My Dog to A Vet?

When Should I Bring My Dog to A Vet

Aside from sore throats and Kennel Cough (which can resolve over time with good rest), all the diseases and conditions mentioned above require immediate appointments with a vet.

The longer you postpone your visits, the harder it will be to properly address and remove the infectious agents from the dog’s system.

What Are Some Home Remedies for My Dog’s Coughs?

Give your furry friend fresh water bowls and a warm, quiet resting place (preferably with humidifiers for easier breathing) to relieve some of his respiratory irritation.

And if you usually take hot showers, why not use that chance to apply some soothing steam therapy on your canine friend?

For collared dogs, I suggest loosening the collar or switching to harnesses during walks. It works when my dog coughs up phlegm


Why is my dog coughing up phlegm? I have listed out some of the most common reasons.

Some of them are quite serious – but not untreatable if using the right treatment methods.

And do not forget to bring your dog to regular check-ups to ensure all unusual coughing symptoms are detected early!


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Hi I am Mitchell. Dog Growth is a blog about dog caring and training where I share my experiences to my community. Hope you enjoy it!

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