A chalazion and a stye are both lumps in or along the edge of an eyelid. In some situations it may be difficult to distinguish between a chalazion and stye.
A chalazion forms when an oil-producing gland in the eyelid called the meibomian gland becomes enlarged and the gland opening becomes clogged with oil. A stye often appears as a red, sore lump near the edge of the eyelid, caused by an infected eyelash follicle. There are many options to treatment for chalazions or styes that do not resolve quickly.