American Dry Cleaner website has a questions and answers section. Alan Spielvogel of the National Cleaners Association and www.nca-i.com answers a question about why a 50/50 poly/cotton blend dark coloured shirt turns brown or rust colour after use due to sweat. The question comes from a person who oversees a moving company. The discolouration happens after the movers where and wash the shirts a couple of times.Spielvogel replies that this is common with golf shirts and polo shirts. The reason why the colour fades on the outside of the shirts rather than the inside is due to acid-sensitive surfer dyes. The dyestuffs reacts with sweat which is what makes the shirts change colour. If there is a discolouration on the outside of the shirt, it is due to the sun on the area, which is causing a bleaching effect along with the reaction from the dyestuffs in the shirts.
If you have this problem with your polo shirts or golf shirts, Spielvogel recommends an alkali-based detergent soak. You can also use a neutral lubricant and ammonia for the soak since it will work just the same.
(c) Evan Welsch,www.sxc.hu