What Is A Large Fluid Filled Lump On A Dog’S Back?

What is a Sebaceous Cyst?

A sebaceous cyst, also known as an epidermal inclusion cyst, is a benign lump or sac under the skin that is filled with sebum. Sebum is an oily substance produced by sebaceous glands in the skin (VCA Animal Hospitals).

Sebaceous cysts commonly develop on the head, neck, trunk and limbs of dogs where there are high concentrations of sebaceous glands and hair follicles. They form when a hair follicle or oil gland becomes blocked, causing sebum to accumulate inside the sac (Kingsdale Animal Hospital).

Sebaceous cysts can range in size from a few millimeters to several centimeters across. They are round or oval in shape and may have a domed, firm appearance. The surface is smooth and they are filled with a cheese-like, foul smelling substance (Toe Grips).

Causes and Development

The exact causes of sebaceous cysts in dogs are not fully understood, but they are believed to have a hereditary component. According to Kingsdale Animal Hospital, sebaceous cysts often result from a buildup of debris or other obstructions in the sebaceous glands, leading to blockage. Additionally, certain breeds like Siberian Huskies, Standard Poodles, and Cocker Spaniels seem predisposed to developing sebaceous cysts, pointing to a potential genetic link.

While sebaceous cysts can occur in dogs of any age, they tend to be more common in middle-aged to senior dogs, usually first appearing when dogs are between 2-8 years old. Trauma or injury to areas with hair follicles and sebaceous glands may also trigger cyst development in some cases.

Overall, the exact causal factors are not definitively known. But genetics, breed tendencies, age, and trauma/injury all seem to play a role in the formation of sebaceous cysts in dogs.


Sebaceous cysts typically appear as smooth, round lumps under the dog’s skin. They are fluid-filled sacs that form below the epidermis and are often described as feeling like a small ball that can be moved under the skin. The lumps are usually painless and the dog shows no signs of discomfort.

However, sebaceous cysts can sometimes rupture and an off-white, cottage cheese-like material will drain from the lump. This material is keratin and cellular debris from inside the cyst. While drainage may provide temporary relief, the cyst can refill with the same material over time if not surgically removed.

In some cases, the cyst may become inflamed, infected, or abscessed. Signs may include redness, swelling, pain, and tenderness around the lump. Dogs may lick or scratch at infected cysts. Prompt veterinary attention is required if the cyst appears irritated or infected.


Diagnosing sebaceous cysts in dogs typically begins with a thorough physical examination by your veterinarian. The veterinarian will look for a raised bump under the skin that may feel firm or fluid-filled. The lump is often hairless and found on the trunk, neck, or upper legs. Your vet may use a needle to draw fluid from the cyst for cytology to confirm it is filled with sebum and not pus or blood, which would indicate an abscess or different type of cyst.

Your veterinarian may also recommend imaging tests like x-rays or an ultrasound to evaluate the size, location, and nature of the cyst. These tests help rule out the possibility of a tumor or deeper structural issue.

Cytology involves examining a sample of the cyst contents under a microscope. This allows your vet to analyze the type of cells present, which helps confirm it is a benign sebaceous cyst.


In many cases, no treatment is necessary for sebaceous cysts on dogs if they are small and not bothering the dog.1 The cysts can be left alone unless they grow, rupture or become irritated. If a cyst does become inflamed or infected, it’s important to keep the area clean until it can be assessed by a veterinarian.

If a sebaceous cyst ruptures, the veterinarian may recommend draining the cyst to help it heal. This involves surgically opening the cyst to drain the fluid, then flushing the area to remove any remaining material. The area is often treated with antibiotics as well to prevent infection.

Surgical removal is commonly recommended for large or problematic sebaceous cysts that are bothering the dog. This eliminates the cyst and prevents future recurrence in that area. While surgery is effective, it may not be ideal for dogs with numerous cysts as removal of each one would require anesthesia and recovery time.2 The location of the cyst also plays a role in determining if surgical excision is the best option.

Surgical Removal

Sebaceous cysts on dogs are often surgically removed by a veterinarian. This is done under general anesthesia in order to keep the dog still and prevent any pain or discomfort during the procedure. The goal of surgical removal is to completely excise the entire cyst wall, making sure no cystic tissue is left behind. If any tissue remains, the cyst can recur after surgery.

Traditionally, a scalpel blade has been used to surgically remove sebaceous cysts, but there are some more minimally invasive options as well. Veterinary laser surgery can also be used to excise the cyst. Another option is cryosurgery, where the cyst is frozen with liquid nitrogen and allowed to slough off on its own. Both laser surgery and cryosurgery have the benefits of less bleeding, swelling, and pain after the procedure.

Regardless of the surgical technique used, the success of sebaceous cyst removal relies on removing the entire cyst wall while minimizing trauma to surrounding tissues. Most veterinary dermatologists and surgeons are experienced in fully excising these growths while preserving normal skin integrity. After surgery, the area will be closed with sutures and the dog will need to wear an Elizabethan collar to prevent licking and chewing at the incision site while it heals.


Home Care

If your dog has a sebaceous cyst that has not ruptured or become infected, there are some at-home care steps you can take:

  • Monitor the size and appearance of the cyst. Note any changes in size, shape, color, or if it begins oozing fluid or blood. Contact your veterinarian if you notice significant changes.
  • Keep the area clean, especially if the cyst ruptures and begins draining fluid or blood. Gently clean with a warm washcloth and pat dry. You can apply an antibiotic ointment if recommended by your vet. This helps prevent infection.
  • Prevent trauma or irritation to the cyst. Avoid letting your dog scratch, lick, or bite the cyst as this can cause it to rupture and become infected. You may need to use an Elizabethan collar.
  • Check for new cysts developing. Some dogs are prone to developing multiple sebaceous cysts.

While home care can help manage sebaceous cysts, surgical removal is often necessary for a definitive cure. Consult your veterinarian to determine the best treatment plan for your dog.


Sebaceous cysts are difficult to prevent. There is no known way to prevent them from occurring in dogs. However, there are some steps that may help reduce the chances of sebaceous cysts developing:

Avoid trauma to the skin – Trauma such as scratches, cuts, and other injuries to the skin can trigger the development of sebaceous cysts. Be gentle when grooming and bathing your dog, and keep their living environment clear of sharp or abrasive objects.

Monitor breeds prone to sebaceous cysts – Some breeds like Cocker Spaniels, Labrador Retrievers, and Poodles seem more prone to developing sebaceous cysts. If you have one of these breeds, monitor their skin regularly for any bumps or lumps that could be early cysts.

There are no known ways to fully prevent sebaceous cysts in dogs. But paying close attention to skin health and avoiding trauma when possible may help reduce risks.


The prognosis for sebaceous cysts on dogs is generally excellent provided the cysts are completely removed. If the sac surrounding the cyst is fully excised during surgery, there is only a 10-15% chance of recurrence. Any remnants of the sac left behind during surgical removal can potentially allow new cysts to form.

For most dogs, sebaceous cysts do not pose an ongoing chronic condition. However, some dogs may be prone to developing multiple cysts throughout their lifetime, especially if underlying factors like genetics, hormone imbalances, or skin allergies are present. Regular monitoring and prompt surgical removal when new cysts arise can help manage the condition. Overall, with proper treatment, most dogs will go on to live normal, comfortable lives.

When to See a Vet

If your dog has a sebaceous cyst, it’s important to monitor it closely and contact your vet if you notice any concerning changes. Here are some signs that indicate it’s time to have your dog seen by a veterinarian:

  • The cyst changes in appearance – grows rapidly, changes color, shape, texture, or oozes fluid
  • The area around the cyst becomes inflamed, red, swollen or develops pus
  • Your dog seems bothered by the cyst, licks or scratches at it excessively
  • The cyst impacts your dog’s movement or mobility
  • The cyst ruptures and fails to heal within a few days

Sebaceous cysts can sometimes become infected or develop into a more serious skin condition. It’s important to have your vet assess any changes to determine proper treatment. They may recommend antibiotics, medicated shampoos, or surgical drainage and removal of the cyst if necessary. Don’t try to drain or remove cysts at home, as this can cause further infection. Contact your vet promptly when you notice the signs above to keep your dog comfortable and prevent complications.

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