Is this mold?

Sure looks like it.

You need to find out if it's coming from moisture in the air - from the shower that looks like there is no exhaust fan in the room- OR if it is coming from the outside walls through the interior.

Wash the walls down with bleach and water. Dry thoroughly. Then wait to see what happens.

Thanks for the quick response. There is no exhaust fan in the bathroom, however, I do keep a window open in there pretty often. I'll try washing the walls down with bleach and water and keep you posted.

It looks like mood to me. Use a bleach and water solution. Spray it on and watch it disappear.

Being that there's no fan, make sure to keep the window and doors open when you clean the walls. I made that mistake once and had trouble breathing and a sore throat for days...

Looks like mold and if it looks like that on the outside it's probably all on the inside of the wall also .. I would take it all out and replace the sheet rock .. Hope you get it taken care of !

That looks like mold to me. You do need to find the source. Important to note that mold can be deadly. Bleach can be used to scrub the infected areas, make sure you're wearing a mask. After cleaning, try to put a fan in there or a heater to dry the area. Bleach works, but not always. You may eventually need to replace it. But more importantly, you need to find out if that mold is coming from the inner wall.

Yes, it is mold and you need to know how to get rid of mold before it can do serious damage. To get rid of the mold fast you have two choices one is you can call up a contractor specializing in mold remediation or you can learn what the contractors know and do it yourself for less. Thanks for sharing these details here, so that everyone can know about this serious issue.