Girls, anyone encountered this? My son has these brown light spots on …

Girls, anyone encountered this? My son has these brown light spots on his back, chest and head. They don't itch, aren't covered in scales. Without bumps. Like birthmarks. Everyone they asked about it. Paid and free clinics. All say it's a contagious rash, supposedly it will pass with time. But I don't see any changes. Don't know which doctor to go to anymore.