A hammer toe is a toe that is deformed, with the end of the toe bending downwards. It usually affects the second, third or fourth toe, and appears to look like a claw. A corn may form on the top of the toe, and a callus may form underneath it. It may be caused by a muscle imbalance or by poorly fitting shoes, when toes are unable to be fully extended. A flexible hammer toe can be manually straightened out while a rigid hammer toe cannot be pulled straight.