A buffer solution can also be called a buffer agent, or acidity regulator. A buffer develops when two substances (a weak acid and its conjugate base, or vice versa) are combined in an aqueous solution. The mixture of these two substances is called a buffer, and when combined in a certain ratio it produces a solution with a specific pH. When a strong base or acid is added to this buffer solution, the pH will remain the same at a practically constant value. Thus, the solution serves a ‘buffer’ to prevent the pH from going up or down. A buffer always consists of weak acids or bases, because they can only react incompletely, which is how the buffer develops.