What causes a stye or chalazion?
Styes are caused by a bacterial infection. Usually the bacteria grow in the root (follicle) of an eyelash. An internal hordeolum is caused by infection in one of the tiny oil glands inside the eyelid.
A chalazion forms when an oil gland in the eyelid becomes blocked. If an internal hordeolum doesn't drain and heal, it can turn into a chalazion.