CONDITION
Sebaceous Cysts
A sebaceous cyst is a small, enclosed pocket that forms in or just beneath the skin, filled with keratin and sometimes oily material. These lumps are typically benign and slow-growing. They are common in dogs, and a dog that develops one is prone to developing more over time. The term is often used broadly to describe several types of skin cysts, though in veterinary medicine the most common are actually epidermoid cysts or follicular cysts, which have slightly different origins but behave similarly. Owners most often notice a firm, round lump under the skin that may remain the same size for months or years, or gradually enlarge. The cyst may feel movable, and occasionally a small pore or opening can be seen on the surface. Some cysts rupture spontaneously, releasing a thick, paste-like substance that can have a distinctive odour, which may prompt concern about infection or something more serious. This page explores what these lumps typically look like and feel like, what is happening beneath the surface, how they are distinguished from other skin masses, and the range of approaches that exist for managing them, including when observation alone may be appropriate and when removal might be considered.
Why this matters now
Sebaceous cysts can develop at any age but become increasingly common in middle-aged and older dogs. They may appear as single masses or multiple cysts may develop over time. Reported predisposed breeds include Boxers, Shih Tzus and Miniature Schnauzers. These cysts often grow slowly over months to years and may go unnoticed until they reach a certain size.
Most sebaceous cysts remain stable and benign, enlarging gradually if at all. Some may rupture spontaneously or following trauma, releasing their characteristic thick, white or greyish contents. Ruptured cysts can become infected, leading to localised inflammation and discomfort. Cysts in areas subject to friction may be more likely to become problematic. Cysts can recur if part of the cyst wall is left behind.
Signals & patterns
Early signals
Small, round, firm lump under the skin
Early cysts present as discrete, well-defined swellings that move with the skin when manipulated.
Smooth surface and regular shape
Unlike some other masses, sebaceous cysts typically have uniform, round contours.
Central pore or dark spot visible
Some cysts have a visible connection to the skin surface appearing as a small dark point.
No pain when touched
Uncomplicated cysts are typically non-tender unless they have become infected or inflamed.
Later signals
Gradual increase in size
Cysts may slowly enlarge over time as sebaceous material continues to accumulate.
Discharge of thick, white-grey material
Rupture releases the characteristic cheesy or waxy cyst contents.
Redness and swelling around the cyst
Infected or inflamed cysts become warm, painful, and surrounded by reactive tissue.
Multiple similar lumps appearing
Dogs prone to sebaceous cysts often develop additional masses in various locations over time.
Click to read about the biological mechanisms
How this is usually investigated
A cyst is often suspected from its appearance and behaviour, but appearance alone cannot rule out a tumour such as a mast cell tumour. Sampling shows what the lump is.
Physical examination
Fine needle aspirate
Expression of contents
Histopathology following removal
Options & trade-offs
Management ranges from monitoring to surgical removal depending on cyst size, location, and whether complications have developed.
Monitoring without intervention
Regular observation of stable, uncomplicated cysts that are not causing problems.
Trade-offs: Appropriate for small, non-problematic lumps once sampling has shown them to be a cyst. Requires periodic reassessment. Does not prevent eventual enlargement or rupture.
Surgical excision
Complete removal of the cyst including its wall to prevent recurrence.
Trade-offs: Removes the cyst for good when the whole wall is taken, and allows histopathological confirmation. Requires anaesthesia. Larger cysts require larger incisions.
Expression and drainage
Emptying cyst contents through the skin opening.
Trade-offs: May provide temporary reduction in size. Cyst typically refills as the wall remains. Not a permanent solution, and squeezing risks a severe inflammatory reaction.
Treatment of ruptured or inflamed cysts
A ruptured cyst sets off a foreign body reaction to the released keratin, which is not always an infection. Anti-inflammatory medication may be used, with antibiotics where bacterial infection is present.
Trade-offs: Settles the acute reaction. Surgical removal may still be needed once inflammation resolves.
Documentation and mapping
Recording cyst locations and sizes for dogs with multiple masses.
Trade-offs: Useful for monitoring multiple cysts. Helps identify new masses or changes in existing ones.
Common misconceptions
"All skin lumps in dogs are harmless cysts"
Many different skin masses occur in dogs, including mast cell tumours, which can look and feel like a harmless lump. Sight and touch cannot tell them apart at home, and a fine needle aspirate is used to find out what a lump is.
"Squeezing out a cyst cures it"
Expression of cyst contents provides only temporary relief. The cyst wall continues to produce material, and the cyst typically refills. Vigorous squeezing can also push keratin into the surrounding tissue and set off a severe foreign body inflammatory reaction. Complete removal requires excision of the entire cyst wall.
"Sebaceous cysts are caused by poor diet or hygiene"
Cyst development relates to individual follicular characteristics and breed predisposition rather than care or diet. They are not a reflection of husbandry.
Related conditions
Lipomas
Lipomas are another common benign skin lump in older dogs and can feel similar to sebaceous cysts on palpation, though lipomas tend to be softer and more moveable, while cysts may feel firmer and are more likely to have a visible surface opening. Both are often monitored rather than removed once sampling has shown what they are, unless they cause discomfort or grow significantly.
Histiocytoma
Histiocytomas are small, firm, dome-shaped lumps that can resemble sebaceous cysts in appearance and texture, particularly in young dogs. The key difference is that histiocytomas tend to appear suddenly and may resolve on their own within weeks to months, whereas sebaceous cysts typically persist and grow slowly over time.
Plasmacytoma
Plasmacytomas can present as solitary, firm lumps in or just beneath the skin, which may be difficult to distinguish from sebaceous cysts by appearance alone. Differentiating between the two often requires sampling of the mass, as plasmacytomas arise from immune cells rather than skin glands.
Pyoderma
When a sebaceous cyst ruptures, the released material and disruption of the skin barrier can create an environment where bacteria multiply, leading to pyoderma (bacterial skin infection). The inflammation and discharge that follow rupture may be mistaken for infection even when bacteria are not the primary cause.
Sterile Nodular Panniculitis
Sterile nodular panniculitis involves inflammation of the fat layer beneath the skin, forming firm lumps that can be confused with deeper sebaceous cysts on palpation. Both conditions may present as non-painful masses, though panniculitis often involves the deeper tissue and may be associated with systemic signs in some cases.
Mast Cell Tumours in Dogs
Mast cell tumours can look and feel like a harmless skin lump, including a cyst, and cannot be told apart by sight or touch. A fine needle aspirate is used to tell the two apart.
Owners noticing new lumps on their dog might note whether the mass is attached to the skin or deeper tissues, whether it has changed over time, and whether it seems to cause any discomfort. For dogs with multiple cysts, keeping a simple map of lump locations can help track changes. A ruptured or inflamed cyst usually reflects a reaction to keratin released into the tissue, and bacterial infection can follow.
Last reviewed: 9 October 2026 · Dr Alastair Greenway MRCVS