Understanding Armpit Lumps: Common Causes and When to See a Doctor

Recurrent pea-sized axillary lumps are common and usually benign, but persistent or progressive lumps require medical assessment.

Differential Diagnosis

1. Reactive Lymphadenopathy (Most Common)

• Causes: Local infection (skin, arm, breast), viral URI, cat-scratch disease, vaccinations (COVID, flu), silicone implants.
• Features: Mobile, tender, <1.5 cm, fluctuate with illness.
• Course: Resolve in 2–4 weeks post-trigger.

2. Folliculitis / Hidradenitis Suppurativa (HS)

• Folliculitis: Infected hair follicles — pustules, erythema; often shaving/deodorant related.
• HS (acne inversa): Chronic follicular occlusion → painful nodules, abscesses, sinus tracts, scarring in axillae/groin. Hurley staging. Requires dermatology.

3. Cysts & Benign Tumors

• Epidermoid cyst: Mobile, central punctum, cheesy keratin; can inflame.
• Lipoma: Soft, doughy, mobile, non-tender.
• Fibroadenoma (axillary tail of breast): Firm, mobile, hormone-responsive.

4. Infectious Abscess

• Fluctuant, erythematous, hot, painful; may drain. Needs I&D + antibiotics.

5. Concerning Features (Malignancy)

• Hard, fixed, non-tender, >2 cm, growing, matted, supraclavicular, associated weight loss/night sweats.
• Metastatic: Breast, lymphoma, melanoma, lung.
• Primary: Lymphoma, soft tissue sarcoma (rare).

When to See a Doctor

• Persists >2–4 weeks
• Continues to enlarge
• Hard, fixed, non-mobile
• Overlying skin changes (erythema, ulceration, peau d'orange)
• Systemic symptoms (fever, night sweats, weight loss)
• Personal history of cancer
• Supraclavicular location (always investigate)

Diagnostic Pathway

1. History & exam (breast, skin, nodes elsewhere)
2. Ultrasound (node architecture: cortex thickness, hilum, vascularity)
3. FNAC or core biopsy if suspicious
4. Excisional biopsy for definitive lymphoma diagnosis

Most axillary lumps are reactive nodes or skin conditions. But "wait and see" has limits—persistent or suspicious features mandate biopsy.