Image on left is from 4 days ago, but the pimple was slowly forming over around 2 weeks.
The goop was sticky, not oily. Earphones are Panasonic RP-TCM130.
I was not able to find an explanation.
Something to increase cable lifespan, lubrication, rubber disintegrating, sweat and earwax that somehow got into the cable, dielectric grease, SCP-1407, no clear answer.
At first I thought the wires just somehow twisted. Nope.
High resistance in a wire inside the sheath would generate more heat at that point, causing the plastic sheath to melt/bubble. So if the wire inside the sheath got damaged, pinched or some of the strands of wire were broken.
These are earbuds, not big ass speakers. There shouldn’t be enough power going through those cables to do melt anything.
Doesn’t explain the goop though