It got the mold because you suctioned it to the wall leaving water trapped inside the cups a breeding ground in a humid bathroom.
Clean mold off rubber bath mat.
Fill the bathroom with hot water and continue until the bath.
You might want to throw it away.
Hand washing is gentler especially on.
Mold is mainly responsible for creating stain the rubber bath mat.
When mold forms on rubber it s important to kill and remove it quickly to prevent long term damage.
Bleach kills mold faster but may discolor or weaken the rubber.
If you let is sit in a bleach solution the mold will eventually fall off with maybe a thorough scrubbing sos pad.
Both vinegar and bleach are effective at killing mold.
Hand wash bath mats that are not machine washable or to just extend the life of the mat bath.
Keep the mat on the floor and close the exit of the water.
To eliminate mold or mildew leave the rubber bath mat in the diluted bleach solution for 3 4 hours.
These stains are likely excess mold and or mildew.
Finally i would give your mat a good soak in vinegar and water at least once every couple months with a good rinse afterward and hang to dry.
This will help stay on top of any mildew or soap scum build up in turn preventing moldy bath mats.
Because rubber is porous the mold may penetrate the surface of the rubber.
Rubber bath mat mold and mildew removal.
Eventually this can cause the rubber to fall apart.
Place the bath mat in the sink or a large bucket of water.
Mix it in a spray bottle and apply to the bath mat stain.
We know that you have lots of questions about cleaning and we want to give you those answers.
When you remove your rubber bath mat from the bathtub to wash it you may notice that your bath mat has left behind stains in your bathtub.
Remove these bath tub stains by making a mixture of 1 cup white vinegar and 2 cups hot water.
Put on rubber gloves and pour a small capful of laundry soap in the water.
Apply bleach on the water and let them.
So at first start the cleaning by removing the mold.
You can wash it in the washing machine cold or warm water please and don t put it in the dryer or you can use borax to clean and disinfect.
How to remove bath mat stains from bathtub.