grease is basically a petroleum based product which may have mineral oil and wax. It may contain other ingredients such as herbs, pathenol, protein, and fragrance.
Its not necesssarily bad for your hair because it depends on the person. However people avoid putting it in their scalp becasue it cloggs pores, and may contribute to dandruff.Usually if someone wants a sclap oil they may choose natural oils such as olive oil, or jojoba oil. I use grease every once in a while on damp hair because it helps seal in the moisture. But if I use it too often it attracts dirt and buildup.