if shirts, once collar become yellow, cannot do anything anymore. i love to wear white shirts/tees. i only hand wash them personally. will scold my wife if she wash them. if any stains i use clorox.

It differs from person to person. Our skin is different.

In general, I'd say no need to wash immediately, but must use some prewash product on the collar/cuffs. Personally I've found it hard nowadays to get one at the major supermarkets, seems like not a popular product anymore. So now I use the one from Daiso. It's not a spray but a liquid. So far so good.

here are what i do:

-usually I will wash the white shirt after wearing it for 1 day, never wear more than 1 day

-if there are stains, I will use Vanish to soak and then wash it