When you sweat you will temporarily lose weight—but this weight is just water weight (water and electrolytes) and not fat weight, and you will put it straight back on as your body is re-hydrated. In addition, as little as a 2% loss of body mass from fluid loss will impair exercise performance. This means a 150-pound student who loses roughly 3 pounds during a heated yoga class from excessive sweating can experience increased heart rate and decreased blood volume, causing a loss of strength and endurance.
Sweat is first and foremost your body’s thermoregulation unit, a means to cool the body down. It essentially will only “cleanse” your skin much in the way a sauna would. “Less than 1% of toxins are lost through sweat” says Dr. Donald Smith, Professor of Environmental toxicology at UC Santa Cruz. Dr. Dee Anna Glaser, professor of dermatology at St. Louis University, and founding member of the International Hyperhidrosis (excessive sweating as a medical condition) Society agrees, “Sweating for the sake of sweating has no benefits and will only release trace amounts of toxins.”