It causes viruses, bacteria, allergens, parasites, fungi, environmental irritants, blocked tear duct, it lasts 2 days to 3 weeks, bacteria about 2 weeks; others - until allergens, irritants or duct blockage is removed. To treat it you should soak eyes separate bed linen and towels to prevent spread of infection, elimination of irritants e.g. tobacco smoke, drops or ointment for bacterial infections, and to relieve discomfort of allergic reaction.
To prevent this you need Good hygiene; avoidance of allergens and other