An ingrown hair cyst is a type of cyst that forms around an ingrown hair. Ingrown hairs occur when a hair curls back and grows into the skin. This can happen anywhere on the body, but it is most common in areas where hair is shaved, waxed, or plucked.
Ingrown hair cysts are usually small, round, and filled with fluid. They can be painful and may cause redness, swelling, and itching. In some cases, ingrown hair cysts can become infected.