Lactic acid causes muscle pain and is life-threatening when produced in high levels. Lactic acid is produced during vigorous exercise or with serious health conditions, such as shock or heart failure. Lactic acid is normally broken down by the liver, and high levels can occur if the liver is damaged.
Lactic acid is produced when the blood is not able to deliver enough oxygen to the muscles. It is typically gone from the body within 60 minutes after exercise. Lactic acidosis occurs when the acid levels are extremely high, but it can also occur in diabetic patients taking metformin who have kidney or heart problems.