A stye or hordeolum is a small, painful lump on the inside or outside of the eyelid. It is actually an abscess filled with pus and is usually caused by a staphylococcus bacteria eye infection.
Styes are common with most people experiencing one or two of them at some stage in their life. Styes are usually visible on the surface but can appear deeper inside the eyelid.
An external stye starts as a small spot next to an eyelash. It turns into a red, painful swelling that usually lasts several days before it bursts and then heals. Most external styes are short-lived and self-limiting.
An internal stye (on the underside of the lid) also causes a red, painful swelling, but its location prevents the familiar whitehead from appearing on the eyelid. The internal stye may disappear completely once the infection is past, or it may leave a small fluid-filled cyst or nodule that can persist and may have to be opened and drained.