What Causes a Stye?
A stye (hordeolum) is caused by bacterial infection of the eyelid glands, most commonly by Staphylococcus species, which invade and infect the oil-producing glands of the eyelid margin. 1
Primary Bacterial Cause
- Staphylococcus aureus is the predominant causative organism responsible for stye formation, with other Staphylococcus species also implicated 1, 2
- The infection specifically targets the meibomian glands (internal hordeolum) within the tarsal plate of the eyelid 1
- These bacteria are part of normal skin flora but cause infection when conditions favor their overgrowth and invasion 1
Mechanism of Infection Development
- Gland obstruction is the critical first step - blockage of the oil glands creates a favorable environment for bacterial proliferation 1
- Once bacteria multiply within the blocked gland, an inflammatory response develops causing the characteristic redness, swelling, and pain 1
- The infection remains localized to the eyelid gland but can spread to adjacent glands if untreated 3
Key Risk Factors That Predispose to Stye Formation
Eyelid-Specific Factors
- Blepharitis (chronic eyelid margin inflammation) creates an environment highly conducive to bacterial overgrowth and subsequent stye formation 1
- Poor eyelid hygiene allows bacterial accumulation on the eyelid margins, increasing infection risk 1
- Meibomian gland dysfunction with chronic blockage predisposes to recurrent infections 1
- Previous history of styes or chalazia significantly increases recurrence risk 1
Contact Lens-Related Factors
- Contact lens wear, particularly with poor hygiene practices or overnight wear, substantially increases stye risk 1, 4
- Contaminated contact lens cases and solutions can harbor bacteria that transfer to the eyelids 1
Cosmetic and Environmental Factors
- Eye makeup can physically block glands and serve as a reservoir for bacterial contamination 1
- Expired or contaminated eye products introduce bacteria directly to the eyelid margin 1
- Frequent eye rubbing transfers bacteria from hands to eyelids 1
Systemic Medical Conditions
- Rosacea increases susceptibility through chronic eyelid inflammation 1
- Diabetes mellitus impairs immune function and wound healing 1
- Immunosuppression from any cause reduces the ability to fight off bacterial invasion 1
- Atopic dermatitis and blepharoconjunctivitis create chronic inflammatory conditions favoring infection 1
Clinical Pitfalls to Avoid
- Do not confuse external hordeolum (stye) with internal hordeolum - both are bacterial infections but involve different gland structures 1, 3
- Recognize that Staphylococcus aureus strains causing eye infections show high rates of multidrug resistance (87% in recent studies), which may complicate treatment if the infection progresses 5
- Be aware that styes can progress to chronic hordeolum or chalazion if the acute infection does not resolve 3