A sty (sometimes spelled stye) is a tender, painful red bump located at the base of an eyelash or under or inside the eyelid. The medical term for a sty is hordeolum (plural, hordeola).
A sty results from an acute infection of the oil glands of the eyelid (meibomian glands) that 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 is responsible for 90%-95% of cases of styes. Staph aureus is frequently found on the skin. A sty can develop as a complication of inflammation of the eyelid.
The term external hordeolum has been used to refer to a sty that develops at the base of an eyelash involving a hair follicle of the eyelid, whereas the term internal hordeolum refers to a sty arising due to an inflamed meibomian gland under the eyelid.
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. In contrast to a sty, a chalazion is usually painless.
The first symptoms of a sty are generally redness, tenderness, and pain in the affected area. The eye may feel irritated or "scratchy." Later symptoms can include swelling, discomfort during blinking of the eye, watering of the eye, and sensitivity to light. A common sign of a sty is a small, yellowish spot at the center of the bump that develops as pus expands in the area.
Styes are very common. People of all ages can develop a sty, and males and females are equally affected. There is a slight increase in incidence of styes during the third to fifth decades of life. People with certain chronic conditions (diabetes mellitus, chronic blepharitis (inflammation of the eyelid), seborrhea, and chronic debilitating illnesses) are more prone to develop styes than the general population. In many susceptible people, stress seems to trigger the development of a sty. Studies have shown that those who have high levels of blood lipids are more susceptible to blockages in the oil glands, including those of the eyelid and, therefore, are more likely to develop a sty.
Application of a warm compress or warm washcloth to the affected area for 10 minutes, four to six times a day, can speed rupture of the sty and aid in the relief of symptoms. A sty should not be pressed or squeezed to facilitate drainage. If a sty persists for several days, a doctor may lance (drain) the infection under local anesthesia in his or her office. Children who require surgical drainage of a sty may need a general anesthetic. Antibiotic ointments and/or steroid ointments sometimes are prescribed to treat a sty. Rarely, systemic (oral) antibiotics are recommended for persistent or multiple styes. OTC pain medications may be used to alleviate pain and tenderness. Contact lenses and eye makeup should never be worn during treatment for a sty.
A sty is harmless in the majority of cases. In most cases, a sty ruptures on its own within a few days to a week, leading to relief from symptoms. Some people will require medical or surgical treatment of a sty, as described in the following section. A sty does not cause intraocular damage (damage to the eye). Styes often recur. Complications of styes are rare (see below).
Complications of a sty are rare. The infection may spread to other eyelash follicles, leading to multiple styes. 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. Chalazia can be large enough to deform the cornea of the eye and interfere with vision, and they may cause a cosmetic problem. Other potential complications include a generalized infection (cellulitis) of the eyelid, and improper drainage of a sty may lead to deformity or disruption of eyelash growth. Progression of a sty to a systemic infection (spreading throughout the body) is extremely rare, and only a few instances of such spread have been recorded.
While it is impossible to completely prevent the development of a sty, good hygienic practices, including proper hand washing, can help prevent all forms of infection, including a sty. Other measures that can help prevent styes include
