ICD-10-CM Code H00.019
Hordeolum externum unspecified eye, unspecified eyelid

An external stye or sty /ˈstaɪ/, also hordeolum /hɔːrˈdiːələm/, is an infection of the sebaceous glands of Zeis at the base of the eyelashes, or an infection of the apocrine sweat glands of Moll. External styes form on the outside of the lids and can be seen as small red bumps. Internal styes are infections of the meibomian sebaceous glands lining the inside of the eyelids. They also cause a red bump underneath the lid with only generalized redness and swelling visible on the outside. Styes are similar to chalazia, but they tend to be smaller and more painful, and they usually don't cause any lasting damage. They contain water and pus, and the bacteria will spread if the stye is forcefully ruptured. Styes are characterized by an acute onset and usually short in duration (7–10 days without treatment) compared to chalazia, which are chronic and usually do not resolve without intervention. Styes are usually caused by the Staphylococcus aureus bacterium.