Hammertoes are a contracture of the toe where your toe bends downward at the joint closest to your foot. It can also be bent downward at the tip of your toe, similar to a mallet toe. The difference between a hammertoe and a club toe is typically the toe does not contract up where it attaches to your foot. Hammertoes are typically caused when the tendons on the top and bottom of your toe are out of balance. This can be hereditary in nature and you could have been born with a foot structure that is unstable, resulting in the deformity.
Hammertoes can also occur from trauma, arthritic processes such as rheumatoid arthritis or osteoarthritis and certain medical conditions that affect the nerves to your feet such as diabetes.