Conjunctivitis, commonly known as pink eye, is an inflammation or infection of the conjunctiva, the thin transparent membrane that covers the white part of the eye and lines the inside of the eyelids. It can be caused by viruses, bacteria, allergies, or irritants such as smoke or chemicals. Symptoms typically include redness, itching, tearing, discharge, swelling of the eyelids, and a gritty sensation in the eye, with bacterial forms often producing thicker discharge. Viral and bacterial conjunctivitis are contagious and spread through direct contact or contaminated surfaces, while allergic conjunctivitis is not contagious. Treatment depends on the underlying cause and may involve supportive care, antihistamines, or antibiotic eye drops, along with good hygiene practices to prevent transmission.