Regarding to your question, there are lots of causes of swollen eyelid. Some causes are mild but some are potentially sight-threatening conditions. When it comes to mild conditions, they are gland blockage, allergies and contact lenses or solutions. However, when you meet the following severe conditions, you are required a immediate medical attention. They are infections,conjunctivitis,orbital celluliti,blepharitis,styes, chalazion and so on. All in all, when your swollen eyelid are cause by bacterial infection or eye disorder, you need to go to see your eye doctor as soon as you can.