Sebaceous cyst under the arm: what to know

The underarm contains skin, hair follicles, sweat glands, lymph nodes, and other soft tissue. An epidermoid cyst may feel like a rounded lump close to the skin, sometimes with a central opening. A swollen lymph node, boil, hidradenitis, or another condition can feel different or similar. Shaving, deodorant, moisture, and friction may aggravate the skin, so appearance and location alone cannot confirm the cause.

Do not squeeze, lance, or repeatedly check the lump. Wash gently, dry the fold carefully, and wear clothing that does not press on it. Pause shaving over irritated skin and avoid products that sting. If a clinician confirms a cyst, treatment may range from observation to an injection for inflammation, drainage of an abscess, or surgical cyst removal. The choice depends on examination findings and whether the lump has returned.

Arrange prompt care for increasing pain, warmth, redness, swelling, pus-like drainage, fever, or redness spreading beyond the lump. Seek assessment for a hard or fixed lump, a lump that enlarges quickly, or one that persists without a clear explanation. Do not assume an underarm lump is a cyst because it is tender or sits near hair.

Could this be a cyst, lymph node, boil, or another skin condition? Should I pause shaving or deodorant? What symptoms would mean I need same-day review?