Lactic acid is a chemical made of lactate and hydrogen ions that acts as an energy source to power your body. Your muscle tissue and red blood cells produce lactic acid when your body breaks down glucose and there's not enough oxygen to create its usual energy.
Lactic acid production is typically tied to intense exercise and is often blamed for muscle soreness after exercise. However, research shows lactic acid doesn't cause sore muscles, and it's also an important source of energy to support cells, tissues, and organs in everyday functions that demand a lot of oxygen.
What Does Lactic Acid Do?
Lactic acid's main functions include:
- Creating energy to power cells when they demand more oxygen than your body gives.
- Turning into new glucose your body can use when it needs more energy.
- Signaling your cells to create an immune response for injuries and infections.
When your body is working hard and can't get enough oxygen to your muscles and tissues, your body starts breaking down glucose (sugars/carbohydrates from food) to create energy. This process is called anaerobic glycolysis.
During anaerobic glycolysis, lactic acid is produced as a byproduct in your muscles. Lactic acid then travels to the bloodstream, separating into lactate and hydrogen ions. Your body reuses lactate as energy before your kidneys and liver filter out extra and turn it into blood sugar (or glucose) for future energy. Producing lactic acid is an alternative process to normal glycolysis—when the body breaks down glucose and uses oxygen to create the energy source adenosine triphosphate (ATP).
Muscle and red blood cells make most of the lactic acid in your body. However, tissues and organs like your skin, brain, and gastrointestinal tract also produce lactic acid. Newer research has also found lactic acid is produced in less oxygen-taxing actions, like regular breathing.
What Causes Lactic Acid Build-up In the Body?
Lactic acid can build up in the body and blood—as lactate and hydrogen ions—when lactic acid is produced faster than your liver and kidneys can break it down. This often happens during intense exercises that require a lot of oxygen, like cardio. The body can usually get lactic acid build-up under control before it causes dangerously high levels.
When your body starts to build up lactic acid during a strenuous workout, you may have temporary symptoms of lactic acidosis (high levels of lactic acid) like:
- Muscle burning or shakiness
- Shortness of breath
Lactic acid build-up is often blamed for muscle soreness a day after exercise. However, this is not accurate. The hydrogen ions in lactic acid are only responsible for temporary muscle discomfort during intense exercise, which will disappear shortly after exercise. Any soreness after working out is actually from small muscle tears or damage that help muscles grow.
How Much Lactic Acid is Bad?
The body typically produces a max lactic acid level of about 20 millimole/killogram per day before it enters your bloodstream. Since lactic acid breaks down into lactate and hydrogen ions in the blood, lactic acid levels are technically measured as lactate levels.
A lactic acid test can help determine if you have too much lactic acid by drawing blood and measuring the lactate levels in your blood. Different lactic acid test levels include:
- Normal lactate levels: Less than 2 millimoles/Liter
- Hyperlactatemia (abnormally high lactate levels): 2 millimoles/Liter to 4 millimoles/Liter
- Severe lactate levels: More than 4 millimoles/Liter (indicates lactic acidosis)
What is Lactic Acidosis?
Lactic acidosis is a life-threatening condition caused by extremely high lactic acid levels in the blood (broken down into lactate and hydrogen). Generally, lactic acidosis occurs when someone has low blood pressure and their tissues aren't getting enough oxygen.
Lactic acidosis symptoms include:
- Muscle weakness
- Shortness of breath
- Abdominal pain
Intense workouts typically don't cause lactic acidosis since the body can resolve high levels before it becomes dangerous. However, certain health conditions can cause two types of life-threatening lactic acidosis: Type A and Type B.
Conditions that cause Type A lactic acidosis, the most common form, include:
- Heart failure
- Lung disease
Conditions that cause Type B lactic acidosis include:
- Overly strenuous exercise
- Diabetic ketoacidosis
- Kidney disease
- Liver disease
HIV medications like nucleoside reverse transcriptase inhibitors (NRTIs) and the type 2 diabetes medication, Metformin, can also make your body create too much lactic acid and increase your risk of developing lactic acidosis.
There is no simple treatment for lactic acidosis. Healthcare providers typically focus on treating the medical condition that caused Type A or Type B lactic acidosis. Treatments that help increase oxygen in the tissues and IV fluids may also help decrease lactic acid levels, but severe lactic acidosis results in death.
How Do You Get Rid of Lactic Acid?
Your body is designed to naturally help you eliminate any excess lactic acid. When you build up too much lactic acid, resulting in lactate and hydrogen ions in your blood, your body can't maintain the same level of intense exercise. As a result, your body will force you to take a break before your lactic acid levels reach dangerous levels. This is when your muscles feel overly weak, you feel sick, or you have that heavy feeling that makes it impossible to keep moving.
When you stop your physical activity and rest, your body can catch up on its usual metabolic processes and remove the extra lactate and hydrogen ions in your blood. Drinking water will also help your body flush out excess lactic acid as your kidneys and liver break it down.
If lactic acid build-up halts your workouts earlier than you'd like, improving your fitness and stamina can help. Being able to withstand intense exercise longer increases the time it takes your body to reach a point of lactic acid build-up, known as your "lactate threshold."
A Quick Review
Lactic acid is an alternative energy source your body produces when there's insufficient oxygen to fuel your cells. Periods of intense exercise—or other situations that demand more oxygen than your body can take in—often use lactic acid for energy.
Your muscles and red blood cells create lactic acid when your body breaks down glucose and there isn't enough oxygen to make its usual energy source, ATP. Instead, your body produces lactic acid to help fuel cells and create future energy when your liver and kidneys break it down into glucose. If lactic acid builds up in the blood—as lactate and hydrogen ions—the body usually signals you to rest before you reach severe levels. However, an underlying health condition can cause high levels of lactic acid that are life-threatening.
Sun S, Li H, Chen J, Qian Q. Lactic acid: no longer an inert and end-product of glycolysis. Physiology. 2017;32(6):453-463. doi:10.1152/physiol.00016.2017
MedlinePlus. Lactic acid test.
Foucher CD, Tubben RE. Lactic acidosis. In: StatPearls. StatPearls Publishing; 2022.
Brooks GA. The science and translation of lactate shuttle theory. Cell Metab. 2018;27(4):757-785. doi:10.1016/j.cmet.2018.03.008
MedlinePlus. Lactic acidosis.
MedlinePlus. Lactic acid test.
Chycki J, Kurylas A, Maszczyk A, Golas A, Zajac A. Alkaline water improves exercise-induced metabolic acidosis and enhances anaerobic exercise performance in combat sport athletes. PLoS One. 2018;13(11):e0205708. doi:10.1371/journal.pone.0205708
Pennington C. The exercise effect on the anaerobic threshold in response to graded exercise. Int J Health Sci. 2015;3(1). doi:10.15640/ijhs.v3n1a14