I looked into this some years ago. Learned that the underarm sweat contains a fatty substance, which doesn't wash out with normal laundering. So concluded that major effort was needed. Boiled the offending garments with washing soda. Big change. Further (and ever better) when we replaced our boiler, we acquired one willing to do more--i.e., go to 140F--and that has made an unbelievable difference in the color of those undershirt underarms. Which, I reason, leads to slower time-to-rot of fabric.
T-shirts! Hubs is always asking me to sew up under arm holes in his. I finally have to say I can’t sew them up again because the fabric is rotted.
I looked into this some years ago. Learned that the underarm sweat contains a fatty substance, which doesn't wash out with normal laundering. So concluded that major effort was needed. Boiled the offending garments with washing soda. Big change. Further (and ever better) when we replaced our boiler, we acquired one willing to do more--i.e., go to 140F--and that has made an unbelievable difference in the color of those undershirt underarms. Which, I reason, leads to slower time-to-rot of fabric.
I switched to black. I only buy him black undershirts now…and yet, he clings to his now-grey arm pits ridden with holes undershirts 🤦♀️.