A bunion is a bony bump that forms on the joint at the base of the big toe. It is caused by a misalignment of the bones in the foot, where the big toe pushes against the other toes, causing the joint to protrude outward. This misalignment can cause the surrounding tissue, including the skin and the bursa (a fluid-filled sac), to become inflamed and painful. As the condition worsens, the big toe may also begin to angle toward the other toes, a condition called hallux valgus. Bunion can be caused by a variety of factors such as genetics, poor foot mechanics, or shoes that do not fit properly.