Deep lines on wrist - what can be causing this and what are my options? (photos)

Hi, Over the past few weeks I have suddenly developed deep lines on my left wrist. I have repeatedly moisturised the lines yet this hasn’t improved. I don’t have any lines on my right wrist and I have added a photo of each wrist. I currently have tan on so you can see that some of the tan has stuck to lines on my left wrist however regardless if I have tan on or not you are able to visible see these lines. What could be causing this and how do I help it. Thank you