While these are probably just normal variations in skin pigmentation, it's odd enough to warrant an exam by a doctor. Could be a fungal infection (doubtful) or something more obscure. Probably not dangerous, but since we don't know what it is, best move would be to have it checked. No sense letting it get worse if it is something.
Hope this helps. Good luck to you.
John Kenyon, EMT, CCT
Non-invasive cardiology tech, Emergency and Critical Care technician, Critical Incident Stress Mgmt. specialist