Sweat as most of us know it is clear, although it can leave yellowish stains on our clothing thanks to those pesky bacteria. If your sweat suddenly came out, say, green, you'd probably think that something was wrong with you. (This would be correct.) Luckily, this rare condition, known as chromhidrosis, isn't typically a sign of a serious problem. It does, however, result in stained clothing, not to mention confusion.
There are two different kinds of chromhidrosis: One affects the apocrine glands, and the other takes on the eccrine glands. People with apocrine chromhidrosis may have black, blue, brown, green or yellow sweat. How does it work? It starts with a pigment granule called lipofuscin, which is produced when unsaturated fatty acids are oxidized in certain types of cells. A buildup of lipofuscin can result in the color being excreted in sweat. Heavily oxidized lipofuscin appears brown or black, while less oxidized granules are lighter. No one knows why some people get this buildup.
Eccrine chromhidrosis is even rarer, and it's caused by eating mass quantities of foods or medications that contain dyes. For example, one often-cited study of a nurse who had reddish sweat showed that she often ate a snack food that listed paprika and tomato powder among its ingredients. (Beware your snacks.)
Treating eccrine chromhidrosis is easy once you've determined what's to blame and cut it out of your diet. Apocrine chromhidrosis treatment is more difficult, since we don't even know why it happens.