Lymph nodes are small, bean-shaped glands that filter fluid and help fight infection. In a healthy dog you can usually feel the ones under the jaw, in front of the shoulders and behind the knees, and they're small, soft and painless.1,2 Swollen lymph nodes have many causes. A single swollen node, especially under the jaw, is often reacting to an infection nearby, such as in the teeth or skin.3,4 When several nodes are enlarged in a dog that otherwise seems well, lymphoma is the most common cause, which is why vets test quickly with a needle sample.5,6,3
See your vet:
- Within a few days if you find several swollen nodes, a node that keeps growing, or a firm, painless swollen node5,6
- The same day if swollen nodes come with fever, lameness, weakness, not eating, unusual bleeding or bruising, or much more drinking and urinating7,8,5
- Now if a swelling in the neck or throat affects breathing or swallowing
If your vet suspects lymphoma, a needle sample comes before any steroid treatment, because steroids can hide the diagnosis.9
What the Research Says
- The pattern matters. A dog with several enlarged nodes is more likely to have lymphoma than a dog with one. Reactive nodes are usually mildly or moderately enlarged, while lymphoma usually causes moderate to marked swelling of several nodes.6
- Lymphoma nodes are often very large. About 80% to 85% of dogs with lymphoma have painless swelling of nodes all over the body, often 3 to 10 times normal size.5
- Not every big node is cancer. In 330 lymph node samples at a Croatian university lab, 38% were lymphoma and another 10% suspected lymphoma; reactive nodes, inflammation and other conditions made up much of the rest.10
- Size alone can mislead. In 100 dogs with mouth melanoma, 40% of normal-sized nodes contained cancer, while 49% of enlarged nodes didn't.11
Where to Feel Your Dog's Lymph Nodes
| Node | Where |
|---|---|
| Mandibular (submandibular) | Under the jaw, toward the back of the jawline. They're further forward and move more easily than the salivary glands just behind them1 |
| Prescapular (superficial cervical) | In front of each shoulder joint1 |
| Popliteal | Behind each knee, in the back of the thigh1 |
| Axillary and inguinal | In each armpit and in the groin2 |
Normal nodes are usually smaller than 1 cm, often under 0.5 cm, and feel soft and painless.1 They're hard to feel in overweight dogs and easier in thin dogs.2 Check both sides of the body and compare. Many more nodes sit inside the chest and belly where you can't feel them.2
Causes of Swollen Lymph Nodes
| Pattern | Common causes | What the vet usually does |
|---|---|---|
| One node, or nodes in one area (for example under the jaw) | Infection or inflammation in the area the node drains, such as the teeth, gums, ears, skin or a wound; sometimes spread from a nearby tumor3,4,11 | Examines the drained area, may take a needle sample, treats the cause and rechecks3,9 |
| Several nodes, dog seems well | Lymphoma most often; also tick-borne disease, body-wide infection or immune disease5,4,3 | Needle samples from two or more nodes, blood tests including calcium, tick tests; flow cytometry or PARR if lymphoma is suspected4,3,5 |
| Several nodes, dog is ill (fever, lameness) | Tick-borne diseases such as Lyme disease and ehrlichiosis, other infections, immune disease; lymphoma is still possible7,12,8,3 | As above, plus infection tests3 |
| One hot, very painful node | An abscess2,9 | Drainage and culture |
Recent vaccination can also make nearby nodes react.6 A soft, fluid-filled swelling under the jaw may be a salivary mucocele rather than a node.1,13 See tick diseases in dogs.
Hard or Soft? What the Feel Can Tell You
- Normal: small, soft, slippery and painless.1,2
- Reactive: mildly enlarged and sometimes a little tender.2,6
- Lymphoma: often firm, painless and much bigger than normal, usually in several places at once.5,2
- Abscess: warm and very painful.2
Feel alone can't tell these apart reliably, so any node that stays enlarged needs a needle sample.2,9
How Vets Find the Cause
- Fine-needle aspirate: a thin needle draws cells from the node to look at under the microscope. It's quick, usually done without sedation and fairly inexpensive, and it often gives an answer.2,6,5 Vets often sample the nodes behind the knee or in front of the shoulder, because the nodes under the jaw often react to mouth and ear problems.4,9
- Biopsy: removing a node or a piece of one under sedation if the needle sample isn't clear. It's the best way to grade lymphoma.5,4
- Flow cytometry and PARR: lab tests on the cells that help confirm lymphoma and show whether it's B-cell or T-cell, which affects treatment and outlook.4,5
- Blood work, tick tests and imaging: blood tests can show high calcium, which goes with some cancers, or signs of infection. Chest X-rays and belly ultrasound check internal nodes.3,2,5
Could It Be Lymphoma?
Lymphoma is one of the most common cancers in dogs. The usual first sign is painless swelling of several lymph nodes in a dog that may still seem well.5,14 Some dogs also drink and urinate more because of high blood calcium.5 Boxers, Golden Retrievers and Rottweilers are at higher risk, mostly in middle age or later.5 Most dogs treated with multidrug chemotherapy go into remission, while untreated dogs usually survive only weeks.15,14 See lymphoma in dogs and signs of cancer in dogs.
Frequently Asked Questions
What does it mean if my dog's lymph nodes are swollen?
The nodes are reacting to something, such as an infection nearby, a tick-borne disease, immune disease or cancer. A single swollen node is often a reaction to a local problem; several swollen nodes need prompt testing.
When should I worry about swollen lymph nodes in my dog?
See your vet within a few days if several nodes are enlarged, a node keeps growing or it feels firm and painless. Go the same day if your dog also has fever, weakness, lameness or bleeding.
Are swollen lymph nodes in dogs always cancer?
No. Infections, tick diseases and inflammation are common causes. But lymphoma is the most common cause when several nodes are enlarged in a dog that seems well, so it should be checked.
Can a dog's swollen lymph nodes go back to normal?
Yes. Nodes reacting to an infection or inflammation usually shrink once the cause is treated. Your vet may recheck them after treatment.
Why is only one lymph node under my dog's jaw swollen?
It's often reacting to a problem in the mouth, teeth, gums or ears. A soft, fluid-filled swelling under the jaw can also be a salivary mucocele rather than a lymph node.
How do vets test a swollen lymph node?
Usually with a fine-needle aspirate, a quick test that takes cells with a thin needle. If that isn't clear, a biopsy or lab tests such as flow cytometry may follow.
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Sources and further reading
This article was rewritten and fact-checked on October 30, 2026 against current veterinary references and specialist guidelines:
- University of Guelph. Peripheral Lymph Nodes. VETM 3430 open textbook, University of Guelph Library (n.d.).
- Podlecki K, DVM. Swollen Lymph Nodes in Dogs. Dogster, updated June 17, 2026.
- Day MJ. Canine lymphadenopathy (proceedings). Hosted by VIN (n.d., references to 2002).
- Selting KA. Lymph Node Cytology: What Should and Should Not Be There. Today's Veterinary Practice, May/June 2014.
- Fan TM. Overview of Canine Lymphoma. Merck Veterinary Manual, Professional Version. Reviewed Sep 2023, modified Apr 2025.
- Wellman M. Cytology of Lymphoid Tumors. SEVC Annual Conference, Barcelona, 2007 (hosted by IVIS).
- Companion Animal Parasite Council. Lyme Disease. CAPC Guidelines, updated May 2019.
- Barnes C, Williams K, Llera R, Ward E. Ehrlichiosis in Dogs. VCA Animal Hospitals, updated July 30, 2025.
- Alleman AR. The Cytological Evaluation of Canine and Feline Lymph Nodes. World Small Animal Veterinary Association Congress Proceedings, 2017 (hosted by VIN).
- Belobrk K, Gudan Kurilj A, Hohšteter M, Huber D, Medven Zagradišnik L, Šoštarić-Zuckermann IC. Cytological examination of canine lymph node: review of diagnostic reports of the Department of Veterinary Pathology, Faculty of Veterinary Medicine in Zagreb over a ten-year period. Veterinar 60(2):23-27, 2022.
- Cray M. Surgical options for oral tumors. MSPCA-Angell, 2023.
- Cornell Richard P. Riney Canine Health Center. Lyme disease. Cornell University College of Veterinary Medicine.
- American College of Veterinary Surgeons. Salivary Mucocele. ACVS, last modified September 20, 2024.
- Hyland K, Weir M, Barnette C. Lymphoma in Dogs. VCA Animal Hospitals (n.d.).
- Penn Vet (Ryan Hospital). Lymphoma in Dogs (client handout PDF, 2025 upload).
About this article
Last updated : new page written using the Merck Veterinary Manual, the University of Guelph, specialist proceedings, Today's Veterinary Practice, a 2022 study of 330 lymph node samples, CAPC and IVIS-hosted proceedings; includes the research summary, where-to-feel table, causes by pattern table, testing, key takeaways and FAQ.
This page is for general information and is not a substitute for an exam by your veterinarian.
