What Causes Pain In Soles Of Feet?

Hi, my daughter, aged 6, was complaining this evening that her soles hurt. I washed her feet with warm water and checked to see if there was any cut or if anything was lodged and then I noticed a tiny black thread like thing on the soles. When I took a closer look, I found that it was a hair growing from her soles. A short, coarse black hair. I pulled it out with a tweezer and the pain went away after that. What actually was it? Should I be worried? Thanks. Ivy