A chalazion is a small lump on the inner or outer surface of the eyelid. It is caused by an inflammatory reaction to material trapped inside an oil-secreting gland in the eyelid. A stye is a lump or pimple on the eyelid edge which represents an infection of an oil or mucous-secreting gland. A chalazion or stye can develop when an eyelid gland becomes blocked. They are often characterized by a red, swollen area of the eyelid.