As I often say to people, Sally, this is the condensation season. Uninsulated sandstone and stone lintels will attract and condense even the slightest bit of water vapour around.
High levels of heating would probably avoid it, but is obviously impractical and uneconomic.
Instead, remove the source of the moisture as much as possible. Rather than a de-humidifier in the kitchen ......... have an extractor fitted ......... the more powerful the better.
Also, in bathrooms, a powerful extractor fitted directly over the shower or bath. Make sure everything is extracted to outside.
Oh, and stop breathing .......... you might want to pass on that one :o)