Also known as a hordeolum, a stye is a small, painful lump on the inner or outer surface of the eyelid. Styes can be caused by an infected eyelash follicle or an infection of meibomian glands, which produce part of the tear film that keeps the eye healthy and moist.

Styes are usually caused by bacterial infections from bacteria such as Staphylococcus, a common bacteria found on the skin and particularly the nose, which can easily be transferred to the eye by rubbing the nose first and then the eye.