A chalazion (plural: chalazia) is an inflammation of the deep oil glands inside the eyelid. It develops over 2 to 3 weeks, forming a painless, firm lump under the skin of the eyelid, sometimes with inflammation and swelling.

Often the cause of a chalazion is not known. It may develop from an internal gland infection that does not drain and heal, or from a blocked oil gland. It can also develop from rubbing the eyes or using products near the eyelid that can irritate the eye.

Home treatment is usually all that is needed for a chalazion. This includes not wearing eye makeup or contact lenses; applying warm, wet compresses to the eye area; allowing the chalazion to break open by itself; and using nonprescription medications. If the chalazion interferes with vision, it may need to be cut open (lanced) by a health professional.