I am a 20-year-old girl. Why do the white socks I have worn turn yellow?

It shows that your feet are sweating a lot, and the fabric of socks is absorbed by sweat, because it is impossible to change it in time when you are away from home, and you can never change it until you get home. After a long time, sweat stains will change color if they are soaked in the fabric for a long time. This principle is the same as that when furniture is used for a long time, but the chemical reaction of yellowing is different.