Water damage near tub, from ?

visiting my friend today to watch the Seahawks game (we won! 5-1 now! woo hoo!) and found that she is worried about this wall damage that has appeared between the toilet and tub/shower. She thinks it is new, but she has only lived there 6 months, and she doesn't usually use that bathroom. It is dry to the touch...but maybe it is wet inside the wall?
-- does this sort of wall damage occur from moisture inside of wall? or outside?
-- toilet supply is a little loose at wall. she turned off supply to toilet, but does that matter? if there was a leak in wall due to the loose supply having damaged a connection in wall, wouldn't it still be leaking in wall despite it being shut off to toilet?
-- her son was using that shower for 3 weeks while staying with her. could this be water damage from shower? this wall is shower head side...and uses a curtain.
so, can we turn the water back on to toilet? do we need to cut into the wall? and to what degree of urgency?
Thank you for your wisdom

It could be from not having the shower curtain in the right passion allowing water to get outside of the tub.

John

A shower curtain will NOT catch water that splashes on the rim of the tub, and then it runs off the edge down the wall causing what you see. To prevent it you have to fasten the little "wings" sold to create a dam at that location and direct the water back into the tub.

Thank you John and HJ. That is a relief!!
so even the large double wrinkle in the center could be caused by that?

so even the large double wrinkle in the center could be caused by that?

Click to expand...

The large double wrinkle could have been caused anytime in the last 110 years.
That may be wall paper back there somewhere.