Understanding Armpit Bumps: Causes and Potential Explanations

Differential for a Quarter-Sized Pink Axillary Lump

1. Hidradenitis Suppurativa (HS)

Chronic follicular occlusion → painful, recurrent nodules/abscesses in axillae, groin, inframammary. Hurley staging. Associated with metabolic syndrome, smoking.

2. Furuncle / Carbuncle (Boil)

S. aureus infection of hair follicle. Tender, erythematous, fluctuant. May drain spontaneously. Risk factors: diabetes, obesity, immunosuppression, nasal carriage.

3. Epidermoid / Sebaceous Cyst

Mobile, non-tender unless infected. Central punctum. Rupture → inflammatory reaction mimicking abscess.

4. Lipoma

Soft, doughy, mobile, non-tender. Slow-growing. Benign.

5. Enlarged Lymph Node

Reactive (local infection, cat scratch, viral), or concerning (lymphoma, metastatic breast cancer, melanoma). Firm, mobile vs fixed/matted.

6. Accessory Breast Tissue

Along milk line; responds to hormonal cycles. May swell premenstrually.

7. Cutaneous Malignancy

• Basal/squamous cell carcinoma
• Melanoma (amelanotic)
• Paget's disease of nipple (rare in axilla)

Red Flags for Urgent Evaluation

• Rapid growth, fixation to deep structures
• Skin ulceration, peau d'orange
• Systemic symptoms (fever, weight loss, night sweats)
• History of breast cancer or melanoma
• Immunosuppression

Diagnostic Pathway

Clinical exam → ultrasound (cyst vs solid, vascularity) → FNA/core biopsy if suspicious → excision biopsy for definitive diagnosis.