Stain Buster Perspiration/Sweat
The best ways to remove perspiration stains

Fabric
Check to see if the stain has changed the color of the fabric. If so, apply ammonia (warning: never mix bleach and ammonia the resulting fumes are hazardous) to fresh stains; white vinegar to old ones. Rinse. Pretreat with a prewash stain remover or rub liquid biological detergent into stain. Wash on the hottest possible setting for that particular fabric. For stubborn stains, add bleach if safe for the fabric.
Upholstery
Mix one teaspoon of washing up liquid and one tablespoon of ammonia with two cups of cool water. Using a clean white cloth, sponge the stain with the detergent/ammonia solution and blot until the liquid is absorbed. Mix one tablespoon of washing up liquid and one tablespoon of white vinegar with two cups of cool water. Sponge the stain with the detergent/vinegar solution and blot until the liquid is absorbed. Using a clean white cloth, sponge the stain with surgical spirit and blot until the liquid is absorbed. Sponge with cold water and blot dry.
Carpet
Although perspiration stains may appear on the back and arms of upholstered furniture, the chances of these stains occurring on your carpet are very slim. In the unlikely event that this happens, use the same method as for upholstery.