Lump It

My veterinarian says my dog has sebaceous cysts. What are they?

Cysts in the skin are one of the more common types of lumps that appear on your dog’s body. A cyst is a small, sac-like nodule located on the surface or within the tissue of the skin. The hollow space inside a cyst may contain fluid or waxy material, depending on the type of cyst. Many of these cysts are noncancerous, but can be prone to secondary bacterial infections.

Cysts often occur inside hair follicles, which are tiny openings that provide a base for the hair or fur to attach. Cysts that involve follicles are known as follicular cysts, and there are several variations. Follicular cysts are characterized by their contents, such as keratin, and by the origination of the cells that make up the lining of the cyst. Most cysts come from glandular tissue like sweat glands. However, in the case of sebaceous cysts, they originate from the sebaceous glands (sweat and oil glands) that are next to the hair follicles.

Sebaceous cysts are one of the most common skin growths seen in dogs. They develop when sebaceous glands release an oily secretion called sebum, which then enters a nearby hair follicle. Usually, sebum plays a role in maintaining the health of the skin, but if it becomes trapped or the body releases too much sebum, a cyst can form.

Why do sebaceous cysts form?

It is believed that sebaceous cysts result from the blockage of a follicle or skin pore. This is because obstructions lead to the accumulation of dead skin cells and secreted glandular materials inside follicles.

Although the true cause of sebaceous-cyst formation in dogs is not completely understood, there are several factors that may increase the risk of cyst formation. Trauma or injuries to the skin, UV ray damage from the sunlight, inflammation or infection, and scar tissue accumulation are all reasons a sebaceous cyst may form.

In hairless breeds, such as the Chinese Crested, Xoloitzcuintle, American Hairless Terrier, and blue-and-fawn Doberman Pinscher, the lack of activity in the hair follicles can lead to the formation of sebaceous cysts. Other breeds, including Schnauzers and Yorkshire Terriers, seem to be genetically predisposed to developing sebaceous cysts.

In some cases, age, sex or the breed of dog is a contributing factor. Different types of sebaceous cysts can be found in older dogs or specific breeds. Sebaceous gland adenocarcinoma is a malignant cyst found in middle-aged and older dogs. These malignant cysts are more likely to be found in male dogs and seen in breeds including Cavalier King Charles Spaniels, Cocker Spaniels, or Scottish, Cairn and West Highland White terriers.

Sebaceous gland adenoma is a rare, benign lesion that can be found in older dogs, typically on the dog’s head. Breeds including Samoyeds, Alaskan Malamutes and Siberian Huskies are predisposed to developing these tumors.

What do sebaceous cysts look like?

A sebaceous cyst appears as a small, raised bump on or beneath a dog’s skin. The cysts are usually single lesions, but it is possible for dogs to have multiple cysts scattered across their body.

The average size of a sebaceous cyst can vary from one-quarter of an inch to two inches wide. They are smooth in appearance, with a white or bluish color, and will sometimes have hair protruding from them because of neighboring hair follicles.

Sebaceous cysts can rupture, so you may not be aware of them until you see bleeding or discharge coming from the area. The discharge is light gray or white in color and may have a “cottage cheese” texture. There is not an odor associated with a ruptured sebaceous cyst unless it has become infected by bacteria.

Should I be concerned if my dog has a sebaceous cyst?

Sebaceous cysts are usually “quiet” in nature and nothing more than a lump you feel when petting your dog. However, if the dog scratches the cyst or it is nicked during grooming, bacteria and yeast on the skin can contaminate the site and cause infection. If the area around the cyst is red, swollen or has an odor, you should have your veterinarian examine your dog.

As mentioned above, it is possible for sebaceous cysts to burst when the cyst becomes too full or does not have enough room to grow. Immediately after rupturing, you may notice discharge or bleeding from the site. It may also be painful for your dog. Ruptured sebaceous cysts require medical attention.

Where do sebaceous cysts tend to occur?

A sebaceous cyst can develop anywhere on your dog’s body. In very young dogs, sebaceous cysts will appear on the top of the head. For dogs of all ages, the most common locations are the head, neck, chest and upper legs.

Dogs can get a similar type of lump on the margin of the eyelid. These occur when secretions from the meibomian gland, a modified sebaceous gland that produces the oil portion of the tear film, build up and form a cyst.

Dogs can also develop sebaceous cysts on pressure points like the elbows. A variety of types of cysts, including sebaceous cysts, may occur on dogs’ paws. This can make walking uncomfortable.

Additionally, some male dogs develop a condition called “stud tail.” It occurs when oily secretions build up from the supracaudal gland. This specialized gland is found at the base of the tail and is composed of sebaceous glands and some sweat glands. While this condition is not a true cyst, cases of stud tail do involve overproduction of sebum and the potential for infection of the gland.

How will my veterinarian diagnose a sebaceous cyst?

Your veterinarian may recommend a fine needle aspirate (FNA). For this procedure, a needle is used to perforate the mass. A syringe is attached to the needle and suction is applied to draw out some contents from the mass into the needle. This material is squirted out onto a glass slide, stained, and then examined under a microscope.

If FNA testing is inconclusive, your veterinarian will recommend a biopsy. While more invasive, biopsies tend to provide more accurate results. Rather than pulling cells from the mass like an FNA, a biopsy involves removing a piece of tissue. This tissue sample is submitted to a pathologist for further examination.

Some sebaceous cysts are small, and a biopsy may mean removing the entire cyst for further analysis. If the pathologist confirms that the margins are clean, the biopsy is considered curative. The biopsy report may come back as a “keratin inclusion cyst,” “follicular cyst” or “epidermal inclusion cyst.” True sebaceous cysts are those filled with sebum only, but these are, for all practical purposes, the same thing.

What is the treatment for sebaceous cysts?

Small but inflamed sebaceous cysts can be managed with antibiotics, anti-inflammatories and topical treatments. If the cyst ruptures, surgical excision is the most effective treatment. Otherwise, the cysts tend to close temporarily, enlarge further and rupture again.

It is important to avoid manually expressing sebaceous cysts. This can introduce bacteria into the cyst when it ruptures. It may also cause an allergic reaction, which happens when the immune system treats the cyst contents like a new infection or foreign substance.

If a sebaceous cyst ruptures, you can use sterile gauze to clean the area and apply firm pressure as needed. Diluted chlorhexidine or betadine solutions are effective for cleaning the wound. Do not apply hydrogen peroxide, as it is harmful to new, healthy cells.

Can sebaceous cysts be prevented?

Good skin health starts with good nutrition. All dogs should eat a properly balanced diet. Diets especially formulated for skin tend to contain extra Vitamin E and omega-3 fatty acids.

Some dogs have excessively oily skin. This is true for hairless dog breeds and dogs that have a condition called seborrhea oleosa, which is a skin disorder where the sebaceous glands release too much sebum. Shampoos and medicated wipes that contain benzoyl peroxide can remove excess oil. Regular brushing of the coat will remove dead fur and skin cells. Frequent exfoliation by grooming is the key to healthy skin.