Your eyelids are lined with glands. These glands make oil to lubricate your eyes. These glands are the culprits behind the terrible red painful bump on your eyelid. Styes are essentially blocked tear glands – instead of making “oil” your glands are making a thicker, more “buttery” consistency oil. So, the gland gets clogged, backed up, swollen, inflamed and quickly turns into a bump.