Most pink eye infections are caused by a virus, and though rarer, other causes also exist such as:
Bacteria in the birth canal passed to a newborn
Extended use of contact lenses
Incompletely opened tear ducts in newborns
There are differences in the various causes of pink eye infection including:
Viral and bacterial eye infection: Associated with colds, as well as respiratory infection and sore throat, and are very contagious. Both children and adults can develop both types, but children are more prone to bacterial.
Allergic eye infection: Affects both eyes and is the body's response to an allergy-causing substance such as pollen. The infection happens because the body produces antibodies in response to the allergens that triggers special cells in the mucous lining of the eyes and airways to release inflammatory substances.
Chemicals or foreign objects: If a chemical or foreign object is splashed into the eye, it can cause pink eye infection because flushing and cleaning the eye to rid it of the chemical or object causes redness and irritation.
Bacteria from the birth canal: Newborns' eyes are susceptible to bacteria normally present in the mother's birth canal. In rare cases, these bacteria can cause infants to develop a serious form of pink eye, which needs treatment without delay to preserve sight. That's why shortly after birth, every newborn's eyes are protected with a preventative application of an antibiotic, such as erythromycin ointment.