A sty
A sty is a red, painful bump that forms either on or inside the eyelid near the edge of the eyelashes.

What is a sty?

A sty (sometimes spelled “stye”) is a red, painful bump that forms either on or inside the eyelid near the edge of the eyelashes. A sty that appears on the outside of the upper or lower eyelid, the more usual location, is called an external sty. A sty that appears on the inside of the upper or lower eyelid is called an internal sty. A sty can look like an acne pimple.

The medical term for a sty is a hordeolum.

A sty is similar to another bump that occurs in the eyelid called a chalazion. A chalazion is a bump that usually occurs farther back on the eyelid. Unlike a sty, a chalazion is usually not painful and is not caused by a bacterial infection. Instead, a chalazion occurs when the opening of the oil-producing glands in the eyelid becomes clogged. Treatment for both conditions, however, is similar.

What causes a sty?

A sty is caused by a bacterial infection in the oil-producing glands in the eyelid. Oil-producing glands line the eyelids and help lubricate the surface of the eye.

What are the signs and symptoms of a sty?

Signs and symptoms of a sty include:

  • Painful red bump along the edge of the upper or lower eyelid near the base of the eyelashes
  • Swelling of the eyelid (sometimes the entire eyelid)
  • Crusting along the eyelid
  • Sensitivity to bright light
  • Sore, scratchy eye
  • Tearing of the eye
  • A feeling that there is something in the eye

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