Conjunctivitis is an illness of the eye. The white of the eye goes red, and the eye often feels sore, itchy, or sticky with a yellow or white film. It can pass from person to person, which is why schools send children home with it. In American English people also call it pink eye — that name just describes the look. Though actually, not every red eye is this illness: smoke, chlorine, tiredness, or an allergy can redden the eye without it being infectious. The ending -itis is a doctor’s way of saying a part of the body is swollen and angry. It is a medical word, but parents and teachers use it freely because the illness is so common in children.