What are hammer toes and what causes this?

Deformity of the toe: They are the buckling of the toe joints and can be caused by injury, short shoes, or heredity.

A contracted toe: A hammertoe is an contracture or a bending of the toe joint which results from a muscle or tendon imbalance due to the mechanical or structural changes in the foot. This can be hereditary or due to environmental factors such as tight shoes. This bending can lead to abnormal pressure distribution resulting in pain, swelling, blistering, and corns.

Bent toe.: People can get hammertoes several different ways, including just an unlucky roll of the genetic dice, but the fundamental result is usually the same: a toe that has drawn back and no longer sits straight or "flat". Sometimes it's only a tendon that holds the toe in that position, other times there's arthritis involved: these tend to be more rigid, and require surgery if you want them corrected.

Hammer toe: These are toes that are contracted at one of the toe joints or both at the lesser toes. It is a result of an imbalance in biomechanics. See your podiatrist for an evaluation as well as a longer explanation than the space here.