Sty Facts: What Causes a Sty?

• A sty (sometimes spelled stye and medically referred to as a hordeolum) is a tender, painful red bump located at the base of an eyelash or under or inside the eyelid.
• Application of a warm compress or warm washcloth to the affected area for 10 minutes, four to six times a day, can speed drainage of the sty and aid in the relief of symptoms.
• Styes are common and are generally harmless.
• A chalazion (a form of scarring of the glands in the eyelid that may include the formation of cysts) is the most common complication that develops from a sty.

A sty (sometimes spelled stye) is a tender, painful red bump located at the base of an eyelash or under or inside the eyelid. A sty results from a localized infection of the glands or a hair follicle of the eyelid. The medical term for a sty is hordeolum (plural, hordeola).

The term external hordeolum refers to a sty that develops at the base of an eyelash (the hair follicle), whereas the term internal hordeolum refers to a sty that develops in a meibomian gland, a gland located on the underside of the eyelid that secretes an oily substance onto the eyeball.

A sty is sometimes confused with a chalazion (see below), which is a cyst or a specific type of scarring due to chronic inflammation arising in the meibomian glands of the eyelid. A chalazion may develop when the infection of a sty persists over time, resulting in scarring around the meibomian gland. In contrast to a sty, a chalazion is usually painless.

A sty results from an infection of the oil glands of the eyelid (meibomian glands) that help to lubricate the eyeball. The infection occurs after these glands have become clogged. A sty also may arise from an infected hair follicle at the base of an eyelash. The bacterium Staphylococcus aureus that is frequently found on the skin is responsible for 90%-95% of cases of styes. A sty also can develop as a complication of diffuse inflammation of the eyelid (blepharitis).

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