Recurring Underarm Cyst Not Due to Ingrown Hair
The most likely diagnosis is a recurring epidermoid (sebaceous) cyst, which should be managed with complete surgical excision of the cyst and its wall once acute inflammation resolves to prevent further recurrence. 1, 2
Understanding the Pathophysiology
- Epidermoid cysts contain keratinous material and normal skin flora even when uninflamed, and inflammation typically occurs as a reaction to rupture of the cyst wall rather than primary infection 2
- These cysts can recur at the same site if the cyst wall is not completely removed during treatment 1, 3
- The axillary (underarm) location is a common site for epidermoid cysts, particularly in hair-bearing areas 3
Immediate Management During Acute Inflammation
- Incision and drainage is the cornerstone treatment when the cyst is actively inflamed and draining 1
- After drainage, cover the surgical site with a dry dressing—this is usually the easiest and most effective approach 1
- Do NOT pack the wound with gauze, as this causes more pain without improving healing 1
- Probe the cavity during drainage to break up any loculations and ensure complete evacuation of contents 1
Antibiotic Use: When and When Not
- Systemic antibiotics are usually unnecessary unless there are signs of systemic infection: temperature >38°C or <36°C, tachypnea >24 breaths/minute, tachycardia >90 beats/minute, or white blood cell count >12,000 or <400 cells/µL 1
- If antibiotics are needed, choose agents active against Staphylococcus aureus, the most common pathogen 1
- Gram stain and culture are NOT recommended as routine practice for inflamed epidermoid cysts 1
Definitive Treatment for Recurrence
- For recurrent cysts at the same site, complete surgical excision of the cyst AND its wall is necessary once acute inflammation has resolved 1, 3
- The cyst wall must be removed completely to avoid relapses—incomplete removal is the primary cause of recurrence 3
- Most cases can be performed under local anesthesia with a low complication rate of approximately 2.2% 3
Differential Considerations
- Search for local causes such as foreign material if cysts continue to recur at the same site 1
- While ganglion cysts can occur in various locations, they are primarily associated with joints and tendons rather than soft tissue of the axilla 4
- Pseudofolliculitis (ingrown hairs) has already been excluded per your question, but would present differently with multiple small papules rather than a single recurring cyst 5
Critical Pitfalls to Avoid
- Do not close the wound without adequate drainage during acute inflammation 1
- Do not attempt definitive excision during active inflammation—wait until the acute episode resolves 1
- Do not assume the cyst is "cured" after simple drainage alone—recurrence is expected without complete excision 1, 3
- Avoid unnecessary antibiotic prescriptions in the absence of systemic infection signs 1