A sty (hordeolum) is a red, painful lump near the edge of your eyelid that may look like a boil or a pimple. Sties are often filled with pus. A sty usually forms on the outside of your eyelid, but sometimes a sty can form on the inner part of your eyelid.
In most cases, a sty will begin to disappear on its own in a few days. In the meantime, you may be able to relieve the pain or discomfort of a sty by applying a warm washcloth to your eyelid.