The picture shows just one hand (the other was holding the camera), but you see how my wrist and thumb are on the machine bed? Even thought I wash my hands before sitting at the machine (thanks, Mom!*) oils and dust accumulate. Even if you can't see it, you may feel it as drag as you sew.
Wipe it down with a gentle cleanser and a soft cloth.
*Mom made us wash our hands before sewing and before playing the piano.