What Causes an Eye Stye?

A stye on the eye is usually caused by a bacterial infection. Risk factors include underlying skin conditions (acne rosacea and seborrheic dermatitis), eye makeup, inflammation of the eyelid (blepharitis), diabetes/medical problems, allergies, and rubbing the eyes.

A stye (also called a hordeolum) on the eye is a small, red, painful lump that forms at the base of an eyelash or under the eyelid. 

Most eye styes are caused by bacterial infections, such as Staphylococcus aureus. Staphylococcus bacteria is commonly found in the nose and does not usually cause problems, but in some cases, if the bacteria are present in your nose and you rub your nose and then your eye, this can transfer the infection to the eye and result in a stye. 

Risk factors for developing a stye include: 

• Underlying skin conditions affecting the eyelids, such as acne rosacea and seborrheic dermatitis
• Eye makeup usage, especially eyeliner or mascara contaminated by bacteria
• Leaving eye makeup on overnight
• Inflammation of the eyelid (blepharitis) 
• Having a stye or chalazion in the past
• Diabetes or other medical problems
• Itchy eyes, such as from allergies
• Rubbing the eyes

A stye may be:

• External 
  • Forms at the base of an eyelash
  • Commonly caused by an infection in the hair follicle
  • May look like a pimple
• Internal 
  • Forms inside the eyelid
  • Usually caused by an infection in an oil-producing gland in the eyelid

A stye is not the same as a chalazion, which also causes a lump on the eyelid. A chalazion is not tender or painful, is not caused by an infection, and it usually lasts longer than a stye.