Don't wash for a month. In the coldest north of China, the temperature is MINUS 10 degrees. I don't wash my socks for three days in summer and one month in winter. My socks stick to my feet, which is particularly itchy. If we scratch them, they are all gray. However, it's ten degrees below zero, and there is no heating in the room. The temperature in the room is only seven or eight degrees. I am shivering with cold every day, and it won't be too sour if I don't wash it for a month.