A hordeolum is a common, painful inflammation of the eyelid margin that is usually caused by a bacterial infection. The infection affects oil glands of the eyelid and can be either internal or external. In many cases, the lesion drains spontaneously and resolves without treatment; however, the inflammation can spread to other ocular glands or tissues, and recurrences are common. If unresolved, an acute internal hordeolum can become chronic, or can develop into a chalazion. External hordeola, also known as styes, were not included in the scope of this review.