I think the first thing I need to explain the definition of a stye and eye infection. Eye infection is a big range of infections, caused by various bacteria or virus, occured to different part of eyes, for example conjunctivitis, iritis, uveitis and so on. As to stye, it is the acute infection of the meibomian glands in eyelids, which is responsible for oil production as part of the tear film in eyes. Because the gland is congested, the oil is building up in the gland which gradually forms a red and painful dump, usually at the root of eyelashes. A stye is common caused by bacterial infection and it would last for months. To judge it is a stye or not, there is alwaya cyst on the eyelids if it is a stye, which in my mind is the basic and simply way to tell. If your symptoms are serious, then it is better to visit the oculist for treatment. Although a stye brings no other harms but ebarrassing and painful, other eye infections might lead to severe results.