Baking powder is a chemical leavener, or raising agent, that contains a mix of baking soda and an acid which will react with the baking soda to begin producing leavening gases. Single-acting baking powder creates gas upon contact with water, double-acting baking powder creates gas upon contact with water as well as again, when heated.
The acid component of baking powder may contain aluminium. There are non-aluminium baking powders available. See: Aluminium
Baking powders often contain anticaking agents such as corn starch; individuals sensitive to such products should be aware.
Self-raising flour, cake mixes, quickbread mixes, batter mixes