Does anyone know of a way to keep yellow pit stains out of white clothes?
The yellow stains are from the chemicals in anti-perspirant. Deodorant (or nothing at all) does not produce the same yellowing. No way around it except to find a product without aluminum-based compounds. To reduce it, you should use the very minimum necessary. More product does not mean more effectiveness. It’s just wasted, and ends up on your clothes. Start with a single swipe on a dry armipt. Do not put on your clothes. Finish getting ready to go, allowing an extra 10-20 minutes of time for the anti-perspirant to dry before you put on your shirt. Another method is to use a white under shirt as a sacrifice. Protects the more expensive dress shirt or polo shirt. Noone but your wife will care if the undershirt pits are stained.