A chalazion is a little swelling or lump that appears on the upper or lower eyelid and is painless. One of the microscopic oil glands (meibomian glands) inside the eyelid is clogged, which is the reason behind it. Meibum, an oil secreted by meibomian glands, lubricates the surface of the eye and keeps tears from drying up too rapidly.
The oil produced by a blocked meibomian gland cannot exit the gland normally. Chalazion formation is the result...