Strange gray stuff

19 TM I hope this is the right sub to ask this question in. So, I’ve noticed that every time I masturbate my fingers have this weird gray stuff on them. It looks like dead skin, but I’m not sure and I don’t know if it’s a normal thing or not. I’ve tried looking it up, but I get no answers and I don’t see anyone else talking about it. So, I’m hoping someone here can help and explain what’s going on.