Blistering paint & mould on external wall

[b21playa]

Hi all

Wondering if someone can help me out. I’ve started to notice paint blistering and black mould spot in a first floor bedroom. This is an external wall which is solid brick construction and render. There is a loft room above and the wall is dry.

Looking outside when it’s raining there isn’t any leaks from gutters etc. internal & external pic attached. There is some sort of lip on the external wall which can be seen, this for reference is about 3/4 way up the internal wall.

What could be causing this and any remedies? Could it be the paint has blown causing water to soak through?

Many thanks in advance

 

[23vc]

Condensation due to humidity inside and cold wall surface. Make sure all kitchens and bathrooms have working extractors etc…

 

[b21playa]

Thanks. Seems strange it’s the only wall in the house with the issue and there’s other external walls. Unfortunately bathroom doesn’t have extractor, but window is left open most of the day