What it is
Alumina, also called Aluminum Oxide, is a crystalline compound of Aluminum and Oxygen.
What it does
Alumina is an abrasive. Its crystals may be used to exfoliate.
In addition, alumina is used as a thickening agent and an absorbent.
Finally, it is also used as an anti-caking agent: it prevents the formation of lumps.
Alumina is generally considered to be safe.