You sweat, but toxins likely stayhttp://www.latimes.com/features/health/la-he-skeptic28jan28,1,5398316.story
"The bottom line:
Sweat does contain trace amounts of toxins, says Dr. Dee Anna Glaser, a professor of dermatology at St. Louis University and founding member of the International Hyperhidrosis Society, a medical group dedicated to the study and treatment of heavy sweating.
But, Glaser, adds, in the big picture, sweat has only one function: Cooling you down when you overheat. "Sweating for the sake of sweating has no benefits," she says. "Sweating heavily is not going to release a lot of toxins."
In fact, Glaser says, heavy sweating can impair your body's natural detoxification system. As she explains, the liver and kidneys -- not the sweat glands -- are the organs we count on to filter toxins from our blood. If you don't drink enough water to compensate for a good sweat, dehydration could stress the kidneys and keep them from doing their job. "If you're not careful, heavy sweating can be a bad thing," she says.
Sweating definitely won't help clear the body of mercury or other metals, says Donald Smith, a professor of environmental toxicology at UC Santa Cruz, who studies treatments for metal poisoning. Almost all toxic metals in the body are excreted through urine or feces, he says. And less than 1% are lost through sweat. In other words, you'll do far more detoxifying in the bathroom than you ever could in a sauna."Compositionhttp://en.wikipedia.org/wiki/Sweat
Sweat contains mainly water. It also contains minerals, as well as lactate and urea. Mineral composition will vary with the individual, the acclimatisation to heat, exercise and sweating, the particular stress source (exercise, sauna, etc.), the duration of sweating, and the composition of minerals in the body. An indication of the minerals content is: sodium 0.9 gram/liter, potassium 0.2 gram/liter, calcium 0.015 gram/liter, magnesium 0.0013 gram/liter. Also many other trace elements are excreted in sweat, again an indication of their concentration is (although measurements can vary fifteenfold): zinc (0.4 mg/l), copper (0.3 - 0.8 mg/l), iron (1 mg/l), chromium (0.1 mg/l), nickel (0.05 mg/l), lead (0.05 mg/l).  . Probably many other less abundant trace minerals will leave the body through sweating with correspondingly lower concentrations. In humans sweat is hyposmotic relatively to the plasma .Antibiotic sweathttp://www.nature.com/nm/journal/v7/n12/full/nm1201-1290.html
Most people don't associate sweat with disease resistance, but a recent report suggests sweating can actually help fight infection. In the December issue of Nature Immunology, Schittek et al. show that human sweat contains an antimicrobial peptide that is active against a wide spectrum of pathogenic microorganisms, including E. coli, E. faecalis, S. aureus and C. albicans. Dermicidin is a 47-amino-acid peptide produced in the sweat glands and secreted into sweat. A proteolytically processed form of the protein is then transported to the skin surface. The authors report that the peptide was found to maintain its activity in the acidic, high-salt concentration conditions characteristic of sweat. Two other antimicrobial peptides, cathelicidins and -defensins, have been previously found to be expressed by skin cells. Dermicidin joins immunoglobulin A, interleukins-1, -6 and -8, and tumor necrosis factor- as immunoproteins detected in human sweat. The peptide may provide one of the first lines of defense against invading microorganisms.