I'm with Julie on the toxins and impurities thing ... that's 99% a marketing ploy. Sweating doesn't "release toxins". Really.
Here's one source for you:
http://www.latimes.com/features/heal...,7913944.story
Quote:
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.
The reason your skin can look better when you sweat is not about toxins - it's about the fact that what causes you to sweat is increased body temp. Increased body temp = increased circulation to the capillaries just under your skin to help cool you down. Increased circulation to the skin = healthier skin. Also when you get hot and sweat, your pores open up. Whatever dirt and dust is in your pores can get "washed" away by the sweat. (This isn't sweating out toxins, though). So you get that healthy glow from increased circulation and the opening of the pores.
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