What is a bunion? A bunion is a bony bump that forms where your big toe meets the ball of your foot. When your toes get crowded and the tip of the big toe gets pushed toward the rest of your toes, the base of the toe starts to grow outward and becomes deformed. Besides being unsightly, which is the main complaint about bunions, they can also be painful. If left untreated, bunions can also cause other foot conditions.