Swollen Lymph Nodes in Dogs — Symptom Assessment Guide

Guide to swollen lymph nodes under the jaw or behind the legs in dogs: what to look for, likely causes (infection vs. lymphoma), home checks, red flags, and when to see the vet.

Quick Assessment

• Is this an emergency?

• Most common cause: reactive (infectious or inflammatory) lymphadenopathy due to local infections, skin wounds, dental disease, or systemic infections.
• When to see a vet right away: rapid enlargement, multiple enlarged nodes with illness, breathing or swallowing difficulty, high fever, or any collapse.

What swollen lymph nodes look and feel like

Lymph nodes (lymph glands) are part of the immune system. When they swell they often feel like lumps under the skin near joints and major anatomic landmarks. Owners commonly find lumps:

• Under the jaw (mandibular lymph nodes) — easy to feel in most dogs.
• In front of the shoulders (prescapular/superficial cervical).
• In the armpit area (axillary) — harder to feel in heavy-coated dogs.
• In the groin (inguinal).
• Behind the knee (popliteal) — small and often overlooked.

• Enlarged and obvious compared with the other side (unilateral or bilateral).
• Soft, warm, and painful — often from infection.
• Firm, rubbery, non-painful, or fixed — more concerning for immune-mediated disease or cancer (including lymphoma or metastatic disease).
• Fluctuant and painful with redness — may indicate an abscess.

Common and less common causes (ranked by likelihood)

(References: Merck Veterinary Manual; VCA Animal Hospitals)

Decision tree: common scenarios and what to do

• If a single node under the jaw is slightly enlarged + your dog has bad breath, drooling or a loose tooth → likely dental infection/abscess → action: schedule dental exam; see vet within 48–72 hours.

• If many nodes (jaw, neck, groin, behind knees) are enlarged + your dog is losing weight, lethargic, not eating → likely systemic disease (lymphoma, systemic infection) → action: see vet same day or next day for bloodwork and cytology/aspiration.

• If one node is rapidly growing over 24–72 hours + is very painful, red, warm, possibly draining → likely abscess or infected node → action: see vet immediately; may need antibiotics and drainage.

• If node is firm, rubbery, non-painful, and persistent for >1–2 weeks with no clear local infection → possible neoplasia (including lymphoma) → action: see vet within a few days for fine needle aspirate (FNA) or biopsy.

• If node is mildly enlarged and dog is otherwise bright, eating, and the swelling began after a bite, scratch, or vaccination → likely reactive → action: monitor 48–72 hours; see vet if it increases or does not improve in a week.

Home assessment steps (how to check, what to measure)

When it’s an emergency (red flags — seek immediate veterinary attention)

• Sudden, rapid enlargement of a lymph node over 24–72 hours.
• Difficulty breathing, swallowing, or noisy breathing.
• Collapse, severe lethargy, or inability to stand.
• High fever ≥104°F (≥40°C) or persistent fever despite cooling measures.
• Severe pain, bleeding, or open draining wounds from the node.
• Multiple nodes enlarged with systemic signs (severe vomiting, diarrhea, unexplained bleeding).

When to schedule a vet visit (non-urgent but needs attention)

• Any node that remains enlarged longer than 7–10 days.
• Node that is growing steadily over several days (48–72-hour doubling or clear increase).
• Firm, rubbery, or immobile nodes without pain.
• Multiple enlarged nodes, or enlargement accompanied by weight loss, decreased appetite, lethargy, vomiting, or increased thirst/urination.
• Any uncertainty about the nature of the lump.

What your vet will likely do (diagnostic steps)

• Physical exam and full history.
• Fine needle aspirate (FNA) of the node for cytology — quick, minimally invasive, usually done in-clinic.
• If FNA is inconclusive, a biopsy might be advised for histopathology.
• Bloodwork (CBC, chemistry) and urinalysis to look for systemic infection or organ involvement.
• Imaging (thoracic radiographs or abdominal ultrasound) if cancer is suspected for staging.
• Tick/flea screens or specific infectious disease tests if exposure is likely.

Home care while monitoring

• Keep your dog comfortable, rested, and well hydrated.
• Avoid squeezing or attempting to lance a lump at home.
• Warm compresses (gentle, 5–10 minutes, several times daily) can help if the node is painful and no open wound is present.
• Prevent licking or chewing the area (use an e-collar if needed).
• Do not give human medications without veterinary approval. Many human pain relievers are toxic to dogs.
• Administer any prescribed medications exactly as directed by your vet.

How to describe the problem to your vet — what to tell them

Prepare this information before your visit or phone call:

• When you first noticed the swelling and how it has changed (size, speed of growth).
• Which node(s) and side(s) are affected (mandibular, prescapular, axillary, inguinal, popliteal).
• Whether swelling is on one side or both sides.
• Your dog’s age, breed, and any previous medical problems.
• Any recent injuries, bites, skin infections, dental problems, or dental procedures.
• Recent travel, boarding, exposure to wildlife, ticks, or fleas.
• Current medications, supplements, and vaccination status.
• Changes in appetite, weight, drinking, urination, stool, energy level, breathing, coughing, vomiting, or other signs.
• Any treatments you’ve tried at home and their effect.

Differentiating normal variation from concerning enlargement (practical tips)

• Compare left vs right — many dogs will have slightly asymmetric nodes, but a clear difference is suspicious.
• Rate of change matters: slow, stable, small increases over weeks may be less urgent than rapid enlargement over 48–72 hours.
• Painful, warm, soft nodes usually suggest infection or inflammation and often improve with appropriate treatment.
• Firm, rubbery, non-painful, and persistent nodes raise concern for neoplasia (like lymphoma) or metastatic disease.
• Generalized (many nodes) vs localized (one node) helps narrow causes: generalized points to systemic disease (including lymphoma), localized suggests a local source of infection or a localized tumor.

Final notes and resources

Swollen lymph nodes are a common finding and most often due to reactive causes such as infection. However, because enlargement can also indicate more serious disease (including lymphoma), it’s important to monitor your dog carefully and consult your veterinarian when the enlargement is persistent, progressive, or accompanied by systemic signs.

Primary sources and further reading:

• Merck Veterinary Manual — Lymphoma in Dogs; Lymphadenopathy: https://www.merckvetmanual.com
• VCA Animal Hospitals — Lymphadenopathy and Lymphoma resources: https://vcahospitals.com

Frequently Asked Questions