Lactic acid is produced by the breakdown of carbohydrates in muscle tissue and red blood cells. It is used by the body during periods when oxygen levels are low.
Lactic acid levels increase when oxygen levels drop due to illness or intense physical activity. Serious conditions, such as heart failure and liver damage, can also increase lactic acid levels. Unusually high amounts of lactic acid may be a sign of lactic acidosis. This condition occurs when too much lactic acid builds up in the bloodstream. A lactic acid test performed by a doctor is critical to determining the cause of high lactic acid levels.