I ran distance -- cross country and two-mile -- in High School in northern AZ and we all had quirks with our feet. Probably because we didn't take care of them the way we should have. Myself, the calluses on the balls of my feet would become great big blisters and take a week or two to recover.
A Navajo friend, Carter, would lose all his toenails. They wouldn't come back until the end of the season.

Looking back, we could have had bigger problems. We were pretty lucky for stupid teenagers -- lessons learned through life, I guess.