Bunions are an enlargement of the bone by the base of the big toe.  The most common cause of a bunion formation is from the genetic type of foot you may have.  Not only does the bone enlarge but it may drift or move out of normal alignment increasing the size and increasing then the pain you may have.  Also, the big toe may become affected and drift toward the smaller toes.  Although bunions are usually hereditary, they can be aggravated by shoe wear, activity, and certain occupations where you stand or walk a lot.  Treatments may include, pads, shoe changes, prescription orthotic supports, and in many cases surgery to re-align the bone and joint.