Hello,
It can be due to bier spots which are small, light macules usually found on the arms and legs of young adult. This is a benign physiologic vascular anomaly of no significance clinically.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.