The ceiling paint on my 1st floor bathroom started bubbling and it has steadily gotten worse, now it has mold over it. (please see the images I took.. sorry they're sideways)

Directly above this bathroom is a 2nd floor bathroom shower. I know this bubbling/mold is caused by water/moisture., but I'm unsure as to which of the following possibilities is the actual cause:

Possibility #1: it's caused by moisture/humidity in the 1st bathroom itself, considering the mold spot is almost right above the shower. perhaps it's just poor circulation in this bathroom?

Possibility #2: it's caused by a leaking pipe (or non-waterproof shower floor?) from the shower from ABOVE on the 2nd floor.

I would greatly appreciate anyone's opinion or advice of expertise on this problem, as I don't want to have to rip open the ceiling if the issue is only poor circulation and can be solved with just a better fan. If the cause IS a leak from above, do you recommend opening the ceiling up from below or completely demolishing the shower floor from above? (only bc the issue may be that they didn't put a waterproof layer under the shower floor?)

Thank you all in advance!!

 

Do you use your bath fan for at least twenty minutes after showering

 

No I usually don't leave the fan on after showering. The fan is on during a shower and then afterwards I leave the bathroom door open to air it out.

 

How old is your home? another possibility is latex paint over oil base enamel ...... but I agree with airman - the exhaust fan needs to be run longer!

 

Yes, run the fan for a longer time. That said, there could be a leak from the bathroom above, I had one when I moved into my house and it caused the paint on the ceiling in my shower stall to fail.