Sweating is supposed to be healthy for you. Helps your body get rid of a lot of those heavy metals, they say.
Maybe try one of those moisture-wicking shirts they sell nowadays, no idea if they help. I've found that it's a bit more comfortable to tuck in the shirt (cotton t-shirt, that is) than to leave it loose. Wear a hat, too - it also helps with sweat containment, along with keeping your ears and neck from being roasted.