Baking powder is a leavening agent, is made by adding some chemical formula soda powder, generally do pastry, add baking powder, can make pastry more fluffy, outside selling steamed buns will generally add baking powder.
This is also why the steamed buns outside look and taste different from those at home. The steamed buns outside are bigger and softer. And the steamed bread at home generally only use yeast fermentation, although soft, but not outside the steamed bread hair.
In fact, when we make cakes normally, baking powder can be put, but the amount of baking powder is only a little, usually 2 or 3g.