I had the same problem, what it is, is dead skin that doesnt come off over time and ends up turning dark...I used lemon juice and scrubbed it off.....always remember, if all else fails, lemon is a good source for everything! When people accidently use too much self tanner, the secret it to use lemon juice to fix the problem...so, like I said, when I was younger, my mom told me to do the lemon juice trick, and it always works...