What Is a Stye?
A stye is a pimple or abscess that forms in either the upper or lower eyelid. The medical term for stye is hordeolum (pronounced HOR-dee-oh-lumm) and it is an infection caused by bacteria that normally live on the surface of the eyelid skin without causing disease. Some of these germs get trapped along with dead skin cells inside crypts along the eyelid margin. Styes are usually superficial and plainly visible. Occasionally they can reside deeper within the eyelid.
An external stye starts as a pimple next to an eyelash. It turns into a red, painful swelling that may last several days before it bursts and then heals. Some external styes are short-lived and self-limiting while others may require the care of your eye doctor.
An internal stye (on the underside of the lid) also causes a red, painful swelling, but its location prevents the familiar whitehead from appearing on the eyelid. The internal stye may disappear completely once the infection is past, or it may leave a small fluid-filled cyst or nodule that can persist and may have to be opened and drained.
Folks tend to confuse a stye with another common lid lump, the chalazion (pronounced cha-LAY-zee-yon). A chalazion is very different from a stye and is not an infection. It is instead a firm, round, smooth, sometimes painless bump usually some distance from the edge of the lid. A chalazion is a local tissue reaction to oily glandular secretions that were unable to reach the lid surface because the duct was blocked by debris.
Styes and chalazia are usually harmless and rarely affect your eyeball or your eyesight but in some cases they can lead to severe infections of the face called cellulitis which can be very serious. They can occur at any age and tend to periodically recur.
What Causes Styes?
Styes are usually caused by staphylococcal bacteria, which often live right on the skin surface. Our bodies are coated with billions of friendly bacteria that coexist with us. When the conditions are just right the bacteria feast on dead cells and other debris, resulting in the tender pimple.
A chalazion is caused by blockage of tiny ducts in the eyelid glands that normally transport an oily substance. This oily material (sebum) is the layer of the tear film that reduces tear evaporation. Trapped or misplaced oil stimulates the immune system to clean up the mess. Chalazia develop over weeks to months.
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