Pink eye is usually caused by viruses, bacteria, allergies, chemicals and irritants, foreign objects in the eye, and possibly a blocked tear duct in newborns. However, the most common causes of pink eye are due to viruses and bacteria. Viral and bacterial pink eye can appear along with the common cold or with symptoms of respiratory infections. Another cause may be due to wearing contact lenses that are not cleaned properly or borrowed from a family member or friend.

Pink eye that is caused by chemicals, irritants, and allergies usually clear up within a few days.