A chalazion is a small, painless lump that forms on the eyelid due to a blocked oil gland. These glands, known as meibomian glands, produce oil that helps keep the eye lubricated. When the gland becomes clogged, it can lead to swelling and the formation of a chalazion. Chalazia can occur in people of all ages and are often confused with styes, which are painful and caused by bacterial infections. While chalazia usually resolve on their own, warm compresses can help speed up the healing process. If they persist, medical treatment may be necessary.