Damp but what kind?

[Oddsocksandmeatballs]

I live in an old house (300 years + old) and we have damp on one wall, there is always a damp spot no matter what the weather and now the paint is peeling. Can anyone help identify what type of damp it is please?

Looks like my walls which give off a kind of salt and make it crumbly. I've been ignoring it, but probably shouldn't