Why Is My Dog’S Lump Oozing Pus?

This article will cover some common reasons why a dog may develop an oozing lump on their body. We’ll discuss what pus is, the most common causes of infected lumps in dogs, when you should take your dog to see the vet, how vets diagnose the cause, treatment options, at-home care tips, when to return to the vet, and prevention of infected lumps. The goal is to provide dog owners with a comprehensive overview of potential causes for their dog’s oozing lump and guidance on caring for their pet.

What is Pus?

Pus is a fluid composed primarily of dead white blood cells, bacteria, inflammatory cells, and proteins. The presence of pus indicates that an area of the body is infected. According to Wikipedia, pus consists of “a thin, protein-rich fluid (historically known as liquor puris) and dead leukocytes from the body’s immune response.”

When bacteria or fungi invade the body and cause an infection, the immune system responds by sending white blood cells, such as neutrophils, to the site of infection. These neutrophils attack and kill the infectious pathogens. However, many of the neutrophils die in the process. The dead neutrophils, along with bacteria, inflammatory cells, and proteins leak into the infected tissue, forming the thick fluid known as pus [1].

Seeing pus is a clear indication that the area is experiencing an active bacterial infection. The presence of pus signals that white blood cells have accumulated to fight an invading pathogen. Pus is often yellow, green or slightly whitish in color, and opaque. The color and thickness of pus can indicate the type of infection.

Common Causes of Infected Lumps

There are various potential causes for an infected lump on your dog that is oozing pus. Some of the most common include:

Bacterial Infections – Bacteria can invade tissues under your dog’s skin through a cut or puncture wound. This causes an abscess to form which fills with pus. Staph and streptococcus bacteria often cause these abscesses.

Infected Anal Glands – Dogs have small sacs on either side of the anus that fill with fluid to help with bowel movements. If these become impacted or infected, it can result in an abscess that oozes pus near the rectum.

Infected Sebaceous Cyst – Cysts are fluid-filled sacs under the skin. They can become infected by bacteria which causes pus to accumulate inside. These are common on the head, back, and tail base.

Infected Histiocytoma – These benign skin tumors are common in young dogs. Though usually harmless, they can sometimes become infected and ooze pus.

Other Causes – Foreign material in wounds, infected insect bites, deep fungal infections, and immune disorders can also lead to infected lumps on dogs.

When to See the Vet

If you notice any lump on your dog that is oozing fluid or pus, it is crucial to schedule an appointment with your veterinarian right away. According to the American Veterinary Medical Association (AVMA), “any abnormal lump or bump on your pet warrants rapid veterinary attention” (AVMA).

An oozing lump indicates there is an infection or abscess present. This requires prompt diagnosis and treatment to prevent the infection from worsening or spreading. Your vet will examine the lump, take samples for testing, and determine the underlying cause. Common causes include bacterial or fungal infections, reactions to insect bites, trauma, blocked pores, or fast-growing masses (AZ Vet).

Depending on the diagnosis, your vet will prescribe antibiotics, anti-fungal medications, draining/removal of abscesses, or other treatment. Leaving an infected lump unchecked allows the infection to burrow deeper into tissue. This makes treatment more difficult and can lead to systemic illness. By bringing your dog in as soon as you notice oozing, your vet can get started on treatment right away to resolve the problem.

Diagnosing the Cause

If your dog has an oozing lump, it’s important to take them to the vet for a proper diagnosis. The vet will first do a physical exam of the lump, noting its location, size, appearance, and whether it seems tender or painful. They may ask about any changes you’ve noticed in the lump’s size, shape, or consistency.

To determine the cause of an oozing cyst or lump, the vet may recommend additional diagnostic tests:

  • Cytology – Taking a sample of the cyst fluid or cells and examining them under a microscope. This can identify if it is a benign cyst or malignant growth.
  • Culture – Swabbing the lump and sending a sample to the lab to test for bacterial or fungal infection.
  • Biopsy – Surgically removing all or part of the lump for pathological examination. This gives the most definitive diagnosis.
  • Blood work – Checking for signs of infection or inflammation. Elevated white blood cell count may indicate an infected cyst.
  • Imaging – X-rays, ultrasound, or MRI to evaluate internal structure of lump and see if connected to underlying tissues.

Determining the type of lump through diagnostic testing is important for deciding on the appropriate treatment plan. Benign sebaceous cysts may only need draining and flushing, while infected or malignant lumps require medications, surgery, or referral to a specialist.

Treating Infected Lumps

If your dog has an infected lump or abscess, your veterinarian will likely prescribe antibiotics to treat the infection. Common antibiotics used include amoxicillin, cephalexin, clindamycin, and enrofloxacin. The antibiotics will help clear up the infection while also reducing inflammation and pain. Draining abscesses is often necessary as well to let the pus and bacteria escape from the lump. Your vet will numb the area before using a scalpel to open and drain the abscess. Flushing out the area with a sterile saline solution helps remove debris. Bandages applied after draining help keep the wound clean while it heals. Anal gland abscesses also need flushing to remove infectious material. Your vet will sedate your dog before inserting a small catheter into the abscess to irrigate it thoroughly. In some cases, the anal glands themselves may need to be removed if they are chronically infected.




Home Care

If your dog has an infected lump that has ruptured or is oozing, it’s important to provide care at home while monitoring the lump. Some tips for home care include:

Keep the area clean. Gently clean around the lump daily using a warm, damp cloth or cotton pad soaked in warm water or an antimicrobial solution like chlorhexidine. Avoid scrubbing or irritating the area. Pat dry afterward.

Apply warm compresses. Place a warm, damp washcloth on the lump for 5-10 minutes, 2-3 times a day. This can help draw out infection and soothe inflammation.

Prevent licking. Dogs’ instinct is to lick at wounds. Use an Elizabethan collar or donut collar to prevent licking, which can introduce more bacteria.

Monitor for changes. Watch for increased redness, swelling, pain, heat, or discharge, which may indicate a worsening infection. Contact your vet if you notice any changes.

With home care and monitoring, many minor infected lumps can heal. However, see your vet promptly if symptoms persist or worsen. They can provide any necessary prescription medications or recommend surgical drainage if needed.


When to Return to the Vet

If the lump continues to ooze pus or fluid after initial vet treatment, it’s important to follow up for further evaluation. Lumps that worsen or fail to improve with antibiotics may require additional testing to identify the underlying cause. Persistent drainage, redness, swelling, or other symptoms mean the infection is not resolving and could spread or cause complications if left untreated.

According to the Texas A&M Veterinary Medical Teaching Hospital article, you should return to the vet if the lump grows rapidly or does not respond to initial treatment. They recommend returning if your dog seems lethargic, stops eating, or shows signs of illness. Prompt vet follow up is recommended if symptoms persist after about 2-3 days of home care and antibiotics.

The Scripps Veterinary Hospital article also advises returning to the vet if a treated cyst continues to refill with fluid and enlarge. This may indicate an ongoing infection or abnormal fluid accumulation that needs further diagnosis. Don’t try to continually drain the lump at home, as this can damage surrounding tissues.

In summary, contact your vet promptly if the lump is worsening or drainage and other symptoms continue despite initial treatment. Catching infections early and following up as needed is key to your dog’s comfort and wellbeing.


There are a few ways pet owners can help prevent infected lumps from developing in their dogs:

  • Take your dog for regular vet checkups and point out any new lumps or changes you notice in existing lumps. Early identification and treatment can help prevent complications like infections.
  • Practice good hygiene around lump sites by gently cleaning with a warm washcloth and veterinarian-recommended cleanser. Avoid harsh scrubbing.
  • Prevent injuries by keeping your home and yard free of sharp objects and other hazards that could cause cuts, punctures or trauma to your dog’s skin.
  • Check your dog’s skin regularly, especially as they age, for any new lumps, bumps or skin changes. Monitor known lump sites for signs of irritation, redness, discharge or swelling.
  • Use an Elizabethan collar to prevent your dog from licking, biting or scratching at lumps. This can prevent infection and rupture.
  • Treat any underlying skin conditions that may make your dog prone to developing lumps.

While not every lump can be prevented, staying vigilant with exams and care can help reduce complications like infections that cause oozing pus.


If your dog has developed a lump that is oozing pus, it’s important not to panic but also not to ignore it. The oozing pus is a sign of infection, which needs to be properly diagnosed and treated. Key takeaways include:

  • Pus is a thick, yellowish fluid that indicates infection.
  • Common causes of infected lumps on dogs include abscesses, cysts, tumors, bug bites, etc.
  • You should make an appointment with your vet as soon as you notice oozing, as the lump likely requires antibiotic treatment.
  • Your vet will diagnose the cause of the lump through a physical exam, medical history review, and possible lab tests.
  • Treatment usually involves draining the infection and prescribing antibiotics and anti-inflammatory medications.
  • At home, keep the area clean and prevent your dog from licking or nibbling the lump.
  • Follow up with your vet until the infection clears up completely.
  • To prevent future infected lumps, control parasites like fleas and ticks, groom your dog regularly, and have lumps evaluated promptly.

While an infected lump can be unpleasant and concerning, the vast majority of cases can be treated successfully under veterinary care. Don’t hesitate to get your dog examined for proper diagnosis and treatment.

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