A chalazion is a lump that forms along the edge of an eyelid. A chalazion often appears as a red, sore lump near the edge of the eyelid, caused by an inflamed oil gland residing near the eyelash follicle. When a stye occurs inside or under the eyelid, it is called an internal hordeolum. Occasionally bacteria can track along the oil gland and cause an eyelid infection known as cellulitis. It is important not to squeeze or try to “pop” a chalazion or stye. This may spread the infection into the surrounding eyelid tissue. Blepharitis is the most common reason for stye formation. Your doctor may prescribe oral and topical antibiotics. Occasionally, the stye must be drained surgically.