Saunas, hot yoga studios, and sweat lodges all swear by the detoxifying effects of sweating. But, in truth, hardly any harmful chemicals come out in your sweat. Sweat is mostly made up of water, plus a certain concentration of sodium, chloride, and potassium, and sometimes proteins and fatty acids. It does include some toxins, but only trace amounts, and those are dwarfed by the quantities that your liver and kidneys constantly flush out of your body. Your body produces sweat primarily to cool you down during exercise or in hot weather.
But if you don't replace that sweat by drinking enough water, you'll get dehydrated, which is the perfect way to stress your kidneys and keep them from doing their job. In other words, sweating doesn't detoxify you, and can actually do the opposite. That's not to say sweating is bad—it's a great way to cool off, as long as you follow it up with a refreshing swig of water.