Patches on external walls

[Firsttimebuyer78]

Hi guys, purchased this property a year and a half ago. These marks have appeared in the past few days and they’re cold but hard. No wetness I can’t figure out what they are. Any suggestions?
They’re all external walls upstairs in a detached house.
Thank you very much!

 

[Wayners]

Cavity walls?

 

[Firsttimebuyer78]

Cavity walls?

Yes cavity walls with no insulation

 

[Koolpc]

Water stains I would suggest. Maybe condensation..

 

[Wayners]

Bit early in the year for condensation but that is what it looks like. Especially now you have confirmed cavity walls.
You would need lots of steam being created or drying clothes in house to get that damp spots.
Funny how they find certain areas but that's what happens.
If you are doing anything to create moisture use a dehumidifier to dry clothes or lower house humidity..
Run for 4+ hours every evening with windows shut