The weather in Guangzhou is easy to be wet and moldy.

Because it is colder indoors than outdoors, the weather is getting warmer, and the building itself has a temperature, and its temperature is low, so when it is cold, the moisture in the air is easily condensed indoors, not the water seeping from the floor and walls (as the saying goes).

So it's best not to open the window. If the door can be opened, it won't open.

Desiccant, activated carbon and dehumidifier can be used.