What should you know about a pus-filled lump in the armpit?

Pus usually forms when the body responds to bacteria or irritation. A boil, infected hair follicle, blocked skin gland or small abscess can cause tenderness, warmth, redness and drainage. Shaving, friction, sweating and skin conditions can contribute. A swollen lymph node can also occur near an infection in the arm, breast or chest, although lymph nodes do not always contain pus. Breast cancer and lymphoma can involve armpit lymph nodes, but a pus-filled lump is not proof of either condition. The clinician may distinguish a skin lesion from a deeper node by examining its position, texture, movement and surrounding skin.

Keep the area clean and cover any drainage with a fresh dressing. A warm, clean compress may ease discomfort. Do not squeeze, pierce or cut the lump, because this can spread infection or injure nearby tissue. Avoid shaving and fragranced products over the area until it settles. Arrange medical review if it is enlarging, painful, repeatedly returning, or not improving. A clinician may need to drain an abscess or prescribe treatment after examining you; do not use leftover antibiotics.

Seek prompt medical help if redness is spreading, pain is rapidly worsening, the skin becomes very hot, or you develop fever, chills, weakness or red streaks extending down the arm. Emergency care is appropriate for confusion, fainting, severe illness or difficulty breathing. Arrange assessment for a firm lump that remains after the skin infection improves, a lump that keeps returning, or a change in the breast, because these findings need a broader examination.

Does this look like a skin abscess, an inflamed follicle or a lymph node? Does it need drainage or a sample? What symptoms should make me return sooner? If it remains after healing, what examination will check the breast and nearby lymph nodes?