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

Last reviewed by a Cleveland Clinic medical professional on 12/26/2017.


  • American Academy of Ophthalmology. What are Chalazion and Styes? Accessed 12/27/2017.
  • Hordeolum: Acute abscess within an eyelid sebaceous gland. Cleveland Clinic Journal of Medicine 2016;May;83(5):332-334.
  • American Academy of Family Physicians. Sty. Accessed 12/27/2017.
  • Lindsley K, Nichols JJ, Dickersin K. Non-surgical interventions for acute internal hordeolum. Cochrane Database of Systematic Reviews 2017, Issue 1. Art. No.: CD007742. DOI: 10.1002/14651858.CD007742.pub4.
  • Vagefi M. Vagefi M Vagefi, M. Reza.Lids & Lacrimal Apparatus. In: Riordan-Eva P, Augsburger JJ. Riordan-Eva P, Augsburger J.J. Eds. Paul Riordan-Eva, and James J. Augsburger.eds. Vaughan & Asbury's General Ophthalmology, 19e New York, NY: McGraw-Hill.

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