sty, in medicine, acute localized infection of one or more of the glands of the eyelid, with pain, swelling, and redness of the lid margin, usually caused by a staphylococcus infection. An external sty usually releases its pus and disappears in a day or so. Hot or cold compresses and antibiotic ointments are used to treat sties. Recurring sties are usually due to uncorrected refractive errors, poor general health, or infection elsewhere in the body. If a sty does not disappear in a few days, a physician should be consulted.

or hordeolum

Infection of an eyelid gland. An external sty results from infection of a sebaceous gland at the edge of the eyelid; tears flow and the eye feels tender, as if something is in it. The sty reddens and swells. Warm compresses help it break sooner. An internal sty is caused by infection of a meibomian gland under the eyelid lining. More painful than an external sty, it usually breaks through the inner lining of the lid when it discharges and may leave a painless cyst (chalazion) at the site. Seealso boil.

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