White Shirt Turned Yellow in Wash

If the stains are on the underarm part of the shirt, that's caused by wearing deodorant. I've heard that smokers usually get these stains because of the nicotine coming out in their sweat, reacting with the deodorant, but I don't know if that's true. Your best bet is to try either soaking in baking soda mixed with water or vinegar.

Try using peroxide to soak the item in. then launder with bluing in the rinse. But don't use too much or it might stain the item blue. Mix the bluing in the water before adding clothing

Bluing is an old remedy that works to remove yellow stains from whites, especially if they are caused by water and washing rather than by something spilled on the item. You can find Mrs. Stewart's Bluing in the laundry section of stores.

You could try washing it by itself with 2-3 Shout Color Catcher Sheets. The package says one, but I have found 2-3 work better. This product is available in the laundry aisle at the supermarket. Air dry the shirt, as the dryer sets stains. Another possibility is Rit's Color Remover. Follow the package directions. Hope this helps.