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 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 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 that may have to be opened and drained.
People tend to confuse a stye with another common lid growth, a 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 develops when an oil duct becomes blocked by debris.
Styes and chalazia (plural of chalazion) are usually harmless and rarely affect your eyeball or 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 recur from time to time.
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 right, the bacteria become overabundant, resulting in the tender pimple.
Chalazia are 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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