Funky gooey stuff on my PS2 controllers. What?

I have two PS2 controllers that came with the console back when I bought it, for years now I've noticed that if either of the controllers are out of use for long enough, the analog sticks somehow emit/accumulate this weird, smelly and sticky goo. Anybody have a clue what's that all about? It feels kinda disgusting when I reach for my controller and instead get a gooey greeting.

Umm... no... that has never happened to me >.> ... maybe your control is possesed

sounds very unpleasant

oily substance on your fingers from handling any food products?

It only starts appearing after about a week of not using the controller, I also wash/wipe my hands if I have any sort of food residue on them because playing with greasy/sticky hands feels disgusting. I was thinking if it, perhaps, absorbs moisture from the air which makes the bacteria react in a way that transforms it into the weird goo, but in that case shouldn't the other buttons have the same problem? I might be overthinking it, but whatever, I'm curious.

ewww, get a new controller! lols

:O That happens to my PS2 controllers too!
I wonder why it happens.

Maybe its glue? very strange