A stye is a small, painful lump (cyst) on the inside or outside of the eyelid.
As styes are usually caused by a bacterial infection, doctors sometimes refer to them as infected eyelid cysts.
The medical name for a stye is a hordeolum.
Styes usually affect one eye, but it’s possible to get them in both eyes or to have more than one stye in the same eye. Your vision shouldn’t be affected.
Styes are usually caused by a staphylococcal infection. Staphylococcus bacteria often live on the skin without causing any harm.