A sty 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 it can form on the inner part of your eyelid.
In most cases, a sty will begin to disappear on its own in a couple 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.
Another condition that causes inflammation of the eyelid is a chalazion. A chalazion occurs when there's a blockage in one of the small oil glands near the eyelashes. Unlike a sty, a chalazion usually isn't painful and tends to be most prominent on the inner side of the eyelid. Treatment for both conditions is similar.