There are many possible reasons for the discoloration, and typically it is nothing to be worried about. Simple changes in pigmentation due to a small trauma, or exposure to a chemical, or a minor skin infection
or other similar things are usually the cause and they are generally not a problem. However, if it is recent, and changing, and spreading, it could be a concern, even very rarely a skin cancer
. So if it is new, you should see your doctor who could do a tiny biopsy
and put your mind at ease. If you are over the age of 50, you should definitely see your doctor, as the risk is higher. I hope this helps, please let me know if you have any more questions.