Hi , this is a really boring question but I have tried everything. I've bought cotton school shirts for my girls from M and S , Next , Tesco , Asda and Sainsburys but always had the same problem.. after a couple of weeks wear ( 2 young teen girls) they go yellow under the arms and when I iron them after washing they stink of sweat just under the arms . My girls wear deodorant and don't sweat profusely, or smell. I use non bio washing powder . Any tips where I'm going wrong ?