Washing Whites
Want to wear white this summer but need to keep it white... Here are a few tips.
Polyester is a breathable and stretchy fabric, which makes it great for sports and athletic wear. White polyester can make your sports gear stand out, on a team or even on the road at night, but it can also start to yellow and look dirty after a few washes. Keeping white polyester sports clothes white is easy with a few extra steps when washing them.
https://www.livestrong.com/article/1005233-keep-white-polyester-sport-clothing-white/
We have a few more tips
For an unwanted stain.
You need fairy washing up liquid. Do not wet the fabric. Pour a small amount of fairy directly on to the stain DO NOT PREWET THE FABRIC. So yes the fabric is dry! Let the green liquid soak in for approximately 3-5 minutes (yes, time it!). Then rinse the stain, which now looks very green (without rubbing the fabric), just keep rinsing with cold water.
This should lift the stain.
https://en.wikipedia.org/wiki/Fairy_(brand)
Don't sweat it. Those yellow stains in the armpits and around the collar of your favorite white T-shirts aren't a sign that you are not cleaning properly.
These areas are just harder to get clean and are made up of just old perspiration and dirt.
Undissolved deodorants may be a culprit, too. If you have hard water, the deodorant residue (and soap and perspiration) can't wash out properly. Here is a method for removing those sweat stains
Mix 1 quart water with 4 tablespoons salt. Sponge this mixture onto the stained area, then repeat until the stain disappears. Wash as usual. This is the recommended technique, I usually just soak in in water with salt for about 30 minutes!