My laundry routine for my dress shirts is washer + 5 mins dryer and hand iron. The shirts are mixed with underwear, socks, and towels. I use Tide Free & Gentle detergent. In the batch I just took out, some of my shirts have this yellowish stain on them. I've gotten this before on a polo shirt, not knowing where it came from. My dry cleaner couldn't take out the stain, so these are really bad news. Anyone know where this is coming from? The washer and dryer are pretty old, could they be leaking something onto my shirts? Edit: I think I've figured out what it is. I left two brass collar stays in the shirts while washing and drying. They're exactly the same color as the stains.