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.

Infants and children up through age 6 to 7 years-old seem to be particularly susceptible to infection with Hemophilus influenzae, and are most at risk. The incidence of severe disease has decreased steadily since the introduction of HiB vaccine (Hemophilus influenzae B). Risk factors include sinus infections or injury to the eyelid including bug bites.