The eyeball can be hurt by infections or allergies. One of the most common threat is conjunctivitis. It is an inflammation of the eye tissue called conjunctiva. The blood vessels of this membrane swell when the conjunctiva is infected. This can cause reddening. Conjunctivitis can occur at any age. Without complications, the conjunctivitis is harmless for visual function. Viral or bacterial infections, allergic reactions, in this review, we will present you the different forms of conjunctivitis and how to treat them.