Medically referred to as a hordeolum, a sty is simply an infection occurring on the eyelid. Sties are caused by the staphylococcal bacteria that normally live harmlessly on the skin of our eyelids but when those germs become trapped inside an eyelash follicle or a tear duct, a painful, pimple-like infection results. In most instances, sties are little more than painful inconveniences but large sties can cause swelling or tearing that interferes with eyesight. In rare cases, multiple sties form along the margin of the eyelid resulting in a potentially serious condition known as blepharitis.

Most sties are "external" and occur on the outside of the eyelid. External sties tend to be short-lived and go away with no lasting damage. "Internal" sties, on the other hand, occur on the underside of the eyelid and often leave pus-filled cysts that have to be drained by a physician. Sties are often confused with another common condition known as chalazia. Chalazia are non-infectious spherical bumps that occur as a result of a blocked duct on the outer surface of the eyelid.

Most sties are self-limiting and go away after about 5 days but you can speed up the healing process by applying hot compresses to the affected area several times a day. After the sty opens, clean the area gently with warm water and a cotton swab several times throughout the day to prevent re-infection or spreading. Most sties can be effectively treated at home but if a sty interferes with your ability to see, tends to reoccur or just doesn't seem to heal, your doctor can prescribe antibiotics.

The best way to prevent sties is simply to wash your hands regularly and avoiding touching your eyes. It's especially important for children, who may rub their eyes when tired or under stress, to be taught to wash their hands after going to the bathroom or finishing an activity. For people with normal immune systems, sties aren't terribly contagious but they can spread from person to person through touch.