Conjunctivitis, commonly known as pink eye, is an inflammation of the conjunctiva, the thin transparent membrane that covers the white part of the eye and lines the inner eyelids. It can be caused by viral or bacterial infections, allergies, or irritants such as smoke or chemicals. Symptoms typically include redness, itching, tearing, discharge, a gritty sensation in the eye, and sometimes crusting of the eyelids, especially upon waking. Viral and bacterial forms are contagious and can spread through direct contact or contaminated surfaces, while allergic conjunctivitis is not contagious. Treatment depends on the cause and may involve supportive care, antihistamines, or antibiotic eye drops, and good hygiene is essential to prevent transmission.