A skin cyst is a small pocket in or under the skin that fills up with material. In dogs, most of them start in a hair follicle [1]. They are common, but a cyst and a tumor can look and feel alike, so any new lump needs a vet’s check.
Do not squeeze a cyst. If a cyst breaks under the skin, the keratin inside spills into the tissue around it, and the body reacts to it as foreign material. That reaction can turn into painful inflammation [1].
Only a vet’s sample can tell a cyst from a tumor. Hair follicle cysts and hair follicle tumors often look much the same under the microscope, and a laboratory check of the tissue is usually what settles it [2]. Do not assume a lump is just a cyst until your vet has checked it.
For other kinds of lumps, see lumps and bumps on dogs.
What a skin cyst is
Most skin cysts in dogs grow from the lining of a hair follicle [1]. The middle of the cyst holds keratin, often in a soft, semi-solid form [1]. Keratin is the tough protein that skin and hair are made of.
Why the name sebaceous cyst is usually wrong
Many people call these lumps sebaceous cysts, as if they came from an oil (sebaceous) gland. In fact, the common cyst forms in a hair follicle, and what fills it is keratin rather than sebum, the oily substance those glands make [1].
Types of skin cysts in dogs
Vets and pathologists sort follicular cysts by the level of the hair follicle they come from and by the kind of keratin they make [1][2]. The names you may see on a laboratory report include:
- Infundibular cysts: from the top part of the follicle, near the skin surface [1][2].
- Isthmus catagen cysts: from the middle part of the follicle [1][2].
- Matrix (matrical) cysts: from the deep, hair-making part of the follicle [1][2].
- Hybrid cysts: cysts that show features of more than one level [1].
- Dermoid cysts: in a large study of skin masses in dogs under one year old, dermoid cysts were among the five most common findings, and boxers were overrepresented [3]. They are related to dermoid sinus, a malformation that is present from birth [6]. See dermoid sinus in dogs, which covers this type in detail.
Fluid-filled cysts from sweat glands
Not every cyst holds keratin. Some come from the apocrine sweat glands, which swell up with fluid. This is uncommon and is seen mostly in middle-aged and older dogs [5]. The cysts tend to appear on the head and neck as soft or tense blisters that can look clear to brownish, usually filled with thin, watery fluid [5]. They can be single or come in groups [5].
Signs of a skin cyst
- A firm lump: follicular cysts are usually single, firm lumps in the skin, and sometimes sit just under it [1].
- More than one: some dogs have several, and in large breeds this has been linked to pressure or rubbing on the skin, for example from lying on hard floors [1].
- Size: a cyst may stay the same size for a long time or slowly get bigger [1].
- Pain: a cyst is often painful when it becomes inflamed [1]. If material comes out on its own, leave it and tell your vet.
- Where: in a study of skin masses sent to a laboratory from dogs under one year old, both dermoid cysts and follicular cysts turned up most often on the belly [3].
Which dogs get skin cysts
Cysts can appear at any age. In the study of dogs under one year old, follicular cysts and dermoid cysts were both in the top five skin masses, and boxers were predisposed to both [3]. In older dogs, too, cysts are among the lumps vets see most: in a Korean study of nearly 3,000 skin biopsies, epidermal and follicular cysts were the single most common group among the skin growths diagnosed [4].
Bumps between the toes have their own causes; see dog paw problems.
When a cyst bursts
When a cyst breaks open under the skin, the keratin and hair inside leak into the tissue around it and set off inflammation [1]. Squeezing a cyst makes this more likely.
A case report from Korea describes two dogs with burst follicular cysts. One had several painful lumps on the front legs; the other had burst, ulcerated and painful lumps near the ear and jaw [1]. In both dogs the leaked keratin caused lumps of inflammation without any infection, a reaction like the one the body mounts against a splinter [1].
A burst cyst that is red, swollen, painful or leaking needs your vet. Do not squeeze it, and do not try to clean it out at home.
How vets diagnose a skin cyst
- Examination: your vet looks at and feels the lump. A lump in or under the skin could be a cyst, an abscess, a growth or something else, so it has to be checked [1].
- Needle sample (cytology): cells are drawn out with a fine needle and looked at under a microscope. This does not always give an answer, and different follicle cysts and tumors often look alike this way [1][2].
- Biopsy or removal and laboratory check (histopathology): a tissue sample, or the whole lump, is checked by a pathologist. This is how the exact type is confirmed [1][2].
Treatment
Surgical removal is the usual treatment for a skin cyst [1]. Removal also lets the lump be checked in a laboratory. A cyst that is intact and causes no trouble may not need to come out straight away, while a painful one is more likely to be removed; surgery can be tricky because the cyst may break [1]. Your vet will advise whether and when to remove a cyst. For a cyst that has burst and caused inflammation, the vet may treat the inflammation as well [1].
At home, as directed by a vet: keep your dog from licking, scratching or chewing the lump, and watch it for changes.
Outlook
Outcomes vary between studies:
- Most skin cysts are not cancer; they are among the commonest benign lumps in dogs [1][4].
- In the two dogs with burst cysts, the inflammation settled with treatment from the vet, and in one dog the remaining cysts were also removed by surgery [1].
These are figures and statements about groups of dogs in particular studies. They do not prove that a treatment caused an outcome, and they cannot predict how one dog will do. Your vet can explain what this means for your dog.
When to see your vet
See your vet if your dog has:
- any new lump, or a lump you have not had checked;
- a lump that grows or changes;
- a lump that bursts or leaks, or is red, swollen or painful [1];
- many lumps at once;
- a lump that your dog licks, scratches or chews at.
FAQ
Can I pop my dog’s cyst?
No. Squeezing can push the keratin inside into the tissue around the cyst, where it can cause painful inflammation [1].
Is it a cyst or a tumor?
You cannot tell by looking or feeling. Your vet takes a needle sample or a biopsy, and some types can only be told apart in a laboratory [1][2].
Is a sebaceous cyst the same as a follicular cyst?
Usually, yes. Most of the lumps people call sebaceous cysts form in a hair follicle and are filled with keratin, not oil [1].
Will a cyst go away on its own?
Surgical removal is the usual treatment, though a quiet, intact cyst may sometimes be watched instead [1]. Your vet can tell you whether your dog’s cyst needs to come out.
Can a cyst come back?
Some dogs get more than one cyst [1]. Ask your vet to check any new lump.
The bottom line
A skin cyst in a dog is a pocket filled with material, usually from a hair follicle. Never squeeze one, because the leaking contents can cause severe inflammation. Only your vet can tell a cyst from a tumor, with a needle sample or a biopsy, so have every new lump checked.
This article is for general information only and does not replace advice from your veterinarian. If you are worried about a lump on your dog, contact your vet.
Sources
- Kim HJ, Cho KO, Baek YB. Foreign body reaction to ruptured follicular cysts in dogs. Vet Med Sci. 2021;7(5):1509-1513. https://pmc.ncbi.nlm.nih.gov/articles/PMC8464301/
- Adedeji AO, Affolter VK, Christopher MM. Cytologic features of cutaneous follicular tumors and cysts in dogs. Vet Clin Pathol. 2017;46(1):143-150. https://pubmed.ncbi.nlm.nih.gov/28249100/
- Kim D, Dobromylskyj MJ, O’Neill D, Smith KC. Skin masses in dogs under one year of age. J Small Anim Pract. 2022;63(1):10-15. https://pubmed.ncbi.nlm.nih.gov/34467541/
- Pakhrin B, Kang MS, Bae IH, et al. Retrospective study of canine cutaneous tumors in Korea. J Vet Sci. 2007;8(3):229-236. https://pubmed.ncbi.nlm.nih.gov/17679768/
- Stazi M, Silvestri S, Mechelli L, Brachelente C. A case of generalised cutaneous apocrine cystomatosis in a Pekingese dog. Vet Med Sci. 2022;8(2):450-453. https://pmc.ncbi.nlm.nih.gov/articles/PMC8959319/
- Torres R, Giovanella C, Sessums K. Type I and type IV dermoid sinus with associated cervical spina bifida in a Labrador Retriever mixed breed dog. Vet Med Sci. 2024;10(1):e1319. Open access, CC BY 4.0. https://pmc.ncbi.nlm.nih.gov/articles/PMC10789649/