There are a number of different causes including the following: Allergy, infections or conjunctivitis and pink-eye, blepharitis (eye lid infection), dry eyes, styes, meibomian cysts, entropion (inward position of the lids), trauma which may be smoke or due to pollution or direct trauma to the eye, sinusitis, allergic rhinitis, facial palsy, age and finally blockage of the drainage system. This blockage often occurs in neonates and usually spontaneously resolves by the age of one. Blockage of the drainage system can be caused by infections, trauma and even stones.