Hole in the center due to the structure of the wart/callus
If you notice a hole in your callus, it may be more than just a regular callus. Often, what appears to be a callus with a hole could actually be a plantar wart. Plantar warts, caused by the human papillomavirus (HPV), commonly develop on the bottom of the foot and can appear similar to calluses. They sometimes have a small hole in the center due to the structure of the wart and clotted blood vessels, which can look like tiny black dots within the wart.
