A chalazion is a hot, red, painful lump under or on the eyelid, which appears within a day or two. Its size may be that of a lentil or a pea, or sometimes even an olive. The chalazion may be on the outside of the eyelid and may be seen easily, but it can also be on the inner side: from the outside, the eyelid is simply red and swollen, and the eyelid must be everted to see the chalazion.