They occur with age, usually after about 40. They're not infectious, and my doctor(s) have said they don't require treatment, but will never go away. Another (online) source said they can be treated, but take a long time to go away.
Chalazion or a meibomian cyst is a condition that arises due to clogging of meibomian gland. Meibomian gland is the gland which produces a sticky substance that helps to keep the eyelashes moist. At times, the duct of meibomian gland may get obstructed and cause the sebum to clog the gland. As a result, small, painless whitish bump may appear on the eyelid. Chalazions are often mistaken for eye stye, but unlike stye, they do not have bacterial origin. Chalazions can also be treated in a similar way as stye, however, they may take quite some time to disappear completely.