A chalazion is a swollen bump on the eyelid. It happens when the eyelid’s oil gland clogs up. It may start as an internal hordeolum (stye). At first, you might not know you have a chalazion as there is little or no pain. But as it grows, your eyelid may get red, swollen, and sometimes tender to touch. If the chalazion gets large, it can press on your eye and cause blurry vision. Rarely, the whole eyelid might swell.