Hello all and thanks for your input!
My Shamisen has an artificial fabric skin on it along the likes of Ripple or Hibiki (not entirely sure what it is exactly as it is second hand). Over time and with prolonged contact (due to bad form my fingers tend to come into direct contact with the skin) some unsightly brown patches are starting to develop on it. I have only taken a damp cloth to it (without much success) for fear of damaging the fabric.
Does anyone have any suggestions of how to get it back to “whiteness” as much as possible?