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Understanding Styes -- the Basics

What Is a Stye?

A stye is a pimple or abscess that forms in either the upper or lower eyelid. It is an infection caused by blockage of an oil duct and bacteria that normally live on the surface of the eyelid without any problems. Some of these germs get trapped along with dead skin cells along the edge of the eyelid. 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 bump that may last several days before it bursts and then heals. Some external styes are short-lived and heal on their own, while others may require the care of your eye doctor.

An internal stye (on the underside of the lid) also causes a red, painful bump, 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 that may have to be opened and drained.

If the clogged gland of a stye never gets better, scar tissue develops around the swollen gland and the pain subsides and a “bump” remains.  That bump is called a chalazion(pronounced cha-LAY-zee-yon). 

Styes and chalazia (plural of chalazion) are usually harmless and rarely affect your eyeball or eyesight, but in rare 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 recur from time to time.

What Causes Styes?

Styes are usually caused by a combination of a clogged oil gland and 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 right, the bacteria become overabundant, resulting in the tender pimple.

Chalazia are the result of a chronic stye when the inflammation runs its course but the painless bump remains. 

WebMD Medical Reference

Reviewed by Alan Kozarsky, MD on March 19, 2014

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