My 10-year-old daughter has developed dark splotches on the front of her neck and also on her forearms. These spots look like dirty skin, but do not come off when scrubbed. I am finding lots of info saying possible diabetes and blood sugar issues, but she doesn't seem to show any other symptoms. SHe is very active/athletic, thin in build, doesn't complain of unusual thirst or frequent urination, and eats relatively heathily. I am curious of any other explanations for this darkening skin.