WebMD states that styes are typically caused by staphylococcal bacteria that live on the skin surface. A lump occurs near the edge of the eyelid when certain conditions cause the bacteria to eat dead skin cells and other materials on the skin.
WebMD describes a stye as a tender swelling near the eyelid. Medical advice is suggested if the stye is painful, styes are recurrent, the stye interferes with vision or the stye does not disappear after a few weeks. Improved eyelid hygiene methods, such as lid scrubs to remove germs and debris or rubbing a soapy solution along the base of the eyelashes, prevent styes.