Blepharitis (blef-uh-RYE-tis) is inflammation of the eyelids. Blepharitis usually affects both eyes along the edges of the eyelids.Blepharitis commonly occurs when tiny oil glands near the base of the eyelashes become clogged, causing irritation and redness. Several diseases and conditions can cause blepharitis.Blepharitis is often a chronic condition that's difficult to treat. Blepharitis can be uncomfortable and unsightly. But it usually doesn't cause permanent damage to your eyesight, and it's not contagious.