it is not an accurate or reliable indicator, but it is an indicator. i stepped on a garden rake recently and painted the wound on my foot. i still went around barefoot and never put a bandage on it. it never got sore. but painting it with logols, the spot remained stained 24/7. and when i quit painting it when it was basically healed, the stain lasted for days. i dont think my body was trying to suck up the Iodine from that spot. it had plenty. and it wasnt evaporating or dissolving int he wet grass i would walk in.