A stye is a painful red bump on the edge of the eyelid that is similar to a boil or a pimple. It is caused by an infection of oil glands in the eyelid, and the bacterium staphylococcus is commonly responsible for most of these infections. The infection occurs when bacteria from the skin, usually staphylococci bacteria, gets into and irritates the oil glands in the eyelids. Touching the eyes with unwashed hands, inserting contact lenses without thoroughly disinfecting them or washing hands first, leaving on eye makeup overnight, and using old or expired cosmetics can increase the risk of developing a stye. Individuals with blepharitis, dandruff, rosacea, diabetes, or high levels of bad cholesterol are also more likely to develop a stye. Styes are often harmless to the eye and will go away on their own within one to two weeks. However, if the stye doesnt start to improve after 48 hours, or redness and swelling involves the entire eyelid or extends into the cheek or other parts of the face, it is important to contact a doctor.