A sty results from an infection of the oil glands of the eyelid (meibomian glands) that help to lubricate the eyeball. The infection occurs after these glands have become clogged. A sty also may arise from an infected hair follicle at the base of an eyelash. The bacterium Staphylococcus aureus that is frequently found on the skin is responsible for 90%-95% of cases of styes. A sty also can develop as a complication of diffuse inflammation of the eyelid (blepharitis).