Cleaning bathroom sink

its common just keep cleaning

In short, mold. Anything that goes down your kitchen drain. Food, soap, gets trapped and gets moldy. I wash the stopper any time I do dishes or even rinse to put in dishwasher. When not in use, take out, turn upside down and dribble dishsoap or vinegar on it, clean,let dry and replace.

Even the cleanest sink gets it. I use an old toothbrush just for sink drains. Soap, shampoo and hand cream build up, but the creamy liquid soap formulas are the worst, along with shaving cream and gel beard softener. The same gunk is building up in your tub and shower drains, but worse because you don't think about cleaning those as often. Best wishes 😇

it is most likely the rubber gaskets on the stopper they just tend to wear

It's a natural thing. Everyone gets it. Just keep cleaning.

I get it too. I spray cleaner around the drain and scrub it off. I use cotton pads , and those and Q tips are amazing for cleaning that gunk.

Here is how I clean mine https://chascrazycreations.com/clean-bathroom-natural-products/

Dead skin and Soap Scum!

Thank you, all, for your comments and suggestions!

You can pull that drain stopper out and clean it. Maybe regularly pour some bleach down it, just because.