An external stye or sty (/ˈstaɪ/), also hordeolum (/hɔrˈdiːələm/), 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 tend to be of smaller size and are more painful and usually produce no lasting damage. Styes are characterized by an acute onset and usually short in duration (7–10 days without treatment) compared to chalazia that are chronic and usually do not resolve without intervention.
