Orbital cellulitis is a dangerous infection with potentially serious complications. It is usually caused by a bacterial infection from the sinuses (ethmoid or para-nasal). Other causes are a stye on the eyelid, recent trauma to the eyelid including bug bites, or a foreign object.

In children, orbital cellulitis is usually from a sinus infection and due to the organism Hemophilus influenzae. Other organisms such as Staphlococcus aureus, Streptococcus pneumoniae, and Beta hemolytic streptococci may also cause this condition.