A chalazion and a stye are both lumps in or along the edge of an eyelid. In some situations it may be difficult to distinguish between a chalazion and stye.
A stye often appears as a red, sore lump near the edge of the eyelid, caused by an infected eyelash follicle. When a stye occurs inside or under the eyelid, it is called an internal hordeolum (pronounced "hor-dee-OH-lum").
The term chalazion (pronounced kuh-LAY-zee-un) comes from a Greek word meaning "small lump." A chalazion forms when an oil-producing gland in the eyelid called the meibomian gland becomes enlarged and the gland opening becomes clogged with oil.
Chalazia tend to develop farther from the edge of the eyelid than styes. Often larger than stye, a chalazia usually isn't painful. It is not caused by an infection from bacteria, and it is not a cancer. Sometimes, when a a stye doesn't heal, it can turn into a chalazion.
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