Common causes of eyelid sties are eyelid inflammation and staphylococcal bacteria, according to Mayo Clinic. Risk factors that may lead to sty formation include leaving makeup on overnight, using expired cosmetics, changing contact lens with dirty hands and failure to disinfect contact lenses before putting them in.
Blepharitis is a condition that causes chronic inflammation on eyelid edges, notes Mayo Clinic, and may result in the formation of sties. Seborrheic dermatitis, also known as rosacea, which is characterized by redness of the face, is an underlying condition associated with blepharitis. A combination of staphylococcal bacteria and a clogged oil gland may also result in the formation of a sty on the eyelid, according to WebMD.