What is Chalazion (Lump in Eyelid)?

A chalazion is a lump of the lid that is caused by obstruction of the drainage duct of an oil gland within the upper or lower eyelid. This lump may increase in size over days to weeks and may occasionally become red, warm, or painful.The gland involved in the formation of a chalazion is a modified oil gland (meibomian gland) that lies within the eyelid. There are about 30-40 of these glands within each of the upper and lower lids. These glands secrete oil into the tears. When one of these glands becomes blocked, it can increase in size and cause a visible lump.Although a stye is also a lump in the eyelid caused by obstruction of an oil gland, a chalazion is not a stye. A stye, or hordeolum, represents an acute infection of the gland. A chalazion is not an infection but is an inflammation of the area. Inflammation is a process in which the body reacts to a condition and produces swelling, redness, pain, or warmth. A stye is usually more painful than a chalazion and may appear infected.

Source: http://www.emedicinehealth.com