Styes in the eye are caused by a bacterial infection, most commonly by the bacteria Staphylococcus aureus. This infection typically occurs when the bacteria infect the oil glands or hair follicles at the edge of the eyelid, leading to a red, tender, and painful lump. The infection can develop in the tiny oil glands in an eyelash follicle (external stye) or in the glands within the eyelid that produce oils to keep the eyelids moist (internal stye).
Common triggers for a stye include touching or rubbing the eyes with hands that have bacteria, using old or contaminated eye makeup, leaving eye makeup on overnight, and poor eyelid hygiene. People who frequently inflame their eyelids (blepharitis), have skin conditions like acne or rosacea, or have diabetes are at higher risk. Stress itself does not cause styes but may increase susceptibility to infection.
In summary, the root cause of a stye is the bacterial infection of the eyelid's oil glands or hair follicles, often facilitated by poor hygiene or irritation of the eyelids.
