A leavening agent (/ˈlɛvənɪŋ/, also leaven agent; /ˈlɛvən/), also known as a raising agent, is any one of a number of substances used in doughs and batters that causes a foaming action that lightens and softens. The leavening agent incorporates gas bubbles into the dough. The alternative or supplement to leavening agents is mechanical leavening by which air is incorporated by mechanical means.