chalazion Although sty is also a lump in the eyelid caused by obstruction of an oil gland, a chalazion is not a sty. A sty, or hordeolum, represents an acute infection of the gland. A chalazion is not an infection but is an inflammation of the area. Inflammation is a process in which the body reacts to a condition and produces swelling, redness, pain, or warmth. A sty is usually more painful than a chalazion and may appear infected.