It's very likely that the "growth" you are concerned about is a callus-or hyperkeratosis as we call it. On occasion, curvey toes will lean into each other and cause pressure and friction that results in the creation of a callus.  These can be so painful, that it's hard to believe it's "just thick skin."  These often occur between the 4th and 5th toes (the baby toe and the one next to it), but can really occur between any two toes.  The technical term for these calluses when they occur on adjacent sides of toes is helomma molle.