Damp spots on carpet

[puds11]

The carpet in my bedroom seems to be developing patches of discolouration. They are small at the moment but seem to be getting more in number. Is it likely to be damp? It doesn’t smell, we do have a heated dryer in the room but also a de humidifier.

Does anyone know what it’s likely to be and the best way to deal with it without removing the carpets

Bump

I had this on a cream carpet. It wasn't damp it was dust from underneath. When carpet was laid In new build the underneath was very dusty so eventually the dust came through