I would like to tell you what it is and how to get rid of it, but I cannot. I had the exact same thing. I went to a doctor (this was when I was younger, maybe preteen and teen) and he gave me these two different things to apply to it. It never worked. In time, it just seemed to go away. I noticed it again maybe twenty years later after a trip to the Phillipines. Again, it disappeared and I have not seen it since. I am under the impression that it may have something to do with sweaty feet due to high temps and/or humidity, but this is just from my own experience.
