Why Do Poly/Cotton Shirts Discolor with Sweat?

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Q: I own a promotional products company in Cincinnati. One of my corporate accounts is a large moving company, and I have golf shirts made in Guatemala for its apparel program. The shirts are a 50/50 poly/cotton blend, and the color is a dark heather — similar to charcoal. After the movers wear and wash them a couple of times, the fabric turns a brown or rust color on the high-sweat areas. The strange thing is that the inside of the shirts look brand-new and don't discolor at all. Do you have any idea why this is happening?

A: This sounds like a problem with acid-sensitive sulfur dyes. This has become a major problem with golf shirts and polo shirts. The dyestuffs react with the acid in the wearer's perspiration, causing orange-colored discolorations. This type of damage can sometimes be corrected by soaking the shirts in an alkali-based detergent or in neutral lubricant and ammonia. Avoid the use of a sour in the laundry formula.

The discoloration may be worse on the outside because sunlight often catalyzes the chemical action of perspiration and can have a degenerating effect on dyestuffs in general.