A skin cyst is a round, noncancerous lump that forms under the skin and can contain fluid, pus, or other materia.

Cyst can occur due to an injury, infection, or other issues. They’re usually benign but may need treatment for complications. A cyst is a sac-like pocket of membranous tissue that contains fluid, air, or other substances. Cysts can grow almost anywhere in your body or under your skin.