What Is Lactic Acid?

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Lactic acid is sometimes used interchangeably with lactate, but lactic acid is lactate joined with hydrogen ions. It is made by muscle tissue and red blood cells during a process that produces energy during physical activity.

This article will explain what lactic acid is, what it does, and what happens if it builds up in the body.

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What Is Lactic Acid?

Lactic acid is a substance made up of lactate and hydrogen ions. It is a byproduct of glycolysis, a metabolic process the body uses during intense physical exercise to produce energy. Lactic acid is made by muscle tissue and red blood cells and forms when the muscles don't have enough oxygen to use other energy sources.

Blood levels of lactic acid are low when there are adequate oxygen levels. When oxygen levels are normal, carbohydrates are broken down into water and carbon dioxide. When oxygen levels drop, carbohydrates are broken down for energy, and lactic acid is formed.

This typically occurs during strenuous exercise, but low oxygen levels can also occur with:

Once the lactic acid leaves the muscle cell, it disassociates into lactate and hydrogen ions, separately occurring in the blood.

While lactic acid is made mainly by muscle tissue and red blood cells, the skin, brain, and intestine also contribute to the approximately 1,500 mM of lactic acid that enters into circulation daily for the average adult.

What Does Lactic Acid Do?

Once the lactic acid leaves the muscle cell and enters the bloodstream, it quickly separates into lactate and hydrogen ions. This lactate can be recycled and used as energy during intense exercise.

The body uses the process of glycolysis to break down glucose into energy for the muscles and other body functions. This occurs most efficiently with aerobic energy production when glucose and oxygen produce adenosine triphosphate (ATP), the body's primary energy source.

If oxygen levels drop too low for aerobic energy production, anaerobic glycolysis occurs, and lactic acid is produced. This is a less efficient means of energy production and happens primarily during intense exercise when energy and oxygen demands are high.

Anaerobic energy production cannot occur for long periods, so it signals to the body that rest is needed. This serves as a protective measure against damage to muscles caused by extreme exertion.

Some research suggests that in addition to energy regulation, lactic acid may play a role in:

  • Immune modulation
  • Memory formation
  • Wound repair
  • Ischemic tissue injury (damage from restricted blood flow)

More studies are needed to understand better how lactic acid impacts the body.

What Is Lactic Acid Build-Up?

When lactic acid is produced faster than the liver can break it down, it can accumulate in the body and blood as lactate and hydrogen ions. While this has the potential to cause damage, the body typically deals with the build-up before problems arise.

Symptoms of Lactic Acid Build Up

Lactic acid build-up can cause temporary symptoms such as:

  • A burning sensation in the muscles
  • Visible muscle shaking
  • Cramping
  • Weakness and/or a feeling of loss of strength or power
  • Shortness of breath

Does Lactic Acid Cause Muscle Soreness After Exercise?

While the hydrogen ions in lactic acid can cause temporary muscle discomfort during strenuous exercise, the muscle soreness felt for a day or two after a workout is not due to lactic acid build-up.

Typically this soreness is from tiny tears and cellular damage within muscle fibers that occur as a result of exercise. While it may feel unpleasant at the time, this is normal and is actually how muscles become bigger and stronger.

How Lactic Acid Build Up Is Treated

The body has built-in ways to handle increased levels of lactic acid. Most importantly, once lactate and hydrogen ions build up in the blood, the body cannot maintain intense exercise. This forces you to rest before your body reaches a dangerous internal imbalance.

Once the exertion stops, the body will clear out the excess lactic acid components on its own without the need to "shake it out" or use other measures to remove it.

Working to increase your physical fitness and stamina over time can help you exercise harder for longer. With any exercise routine, start slow and build as you are ready.

Other things that may help build your tolerance for intense exercise include:

  • Warming up before strenuous exercising
  • Staying hydrated
  • Allowing for periods of rest between workouts
  • Getting an adequate amount of magnesium in your diet
  • Eating foods that meet the nutritional needs of cellular processes
  • Balancing high and low-intensity workouts throughout your week

What Is a Lactic Acid Test?

A lactic acid test may be performed to:

  • Diagnose lactic acidosis
  • Determine if the body's tissues are receiving enough oxygen
  • Look for sepsis (a dangerous reaction to a bacterial infection)
  • Help determine if meningitis is bacterial or viral

The test is done using a blood sample from a vein or artery. If meningitis is suspected, a test for lactate in cerebrospinal fluid may also be performed.

Lactic Acidosis

Very high lactic acid levels can result in a life-threatening condition called lactic acidosis. The type of lactic acidosis depends on the condition that is causing it.

Conditions that can cause type A (most common) include:

Conditions that can cause type B include:

  • Diabetic ketoacidosis
  • Liver disease
  • Kidney disease
  • Leukemia
  • Extremely strenuous exercise/extreme overheating

Certain medications can increase the risk of lactic acidosis, including:

Symptoms of lactic acidosis include:

  • Muscle weakness
  • Nausea/vomiting
  • Shortness of breath
  • Rapid breathing
  • Excessive sweating
  • Cool, clammy skin
  • Abdominal pain
  • Sweet-smelling breath
  • Confusion
  • Coma

When to See a Healthcare Provider

See a healthcare provider if you are showing signs of lactic acidosis. It's also a good idea to see a healthcare provider if you are not recovering well or if muscle soreness continues longer than expected after strenuous exercise. While this may not be directly related to lactic acid, it may indicate injury or a sign that your exercise program needs to be adjusted.


Lactic acid is a substance made up of lactate and hydrogen ions. It is primarily produced by muscle tissue and red blood cells.

Lactic acid is produced during strenuous exercise to help with energy production when oxygen levels are lowered.

The lactic acid build-up is usually temporary and resolves quickly with rest.

Some conditions and medications can lead to dangerously high levels of lactic acid, called lactic acidosis. Unlike typical lactic acid build-up from exercise, lactic acidosis is life-threatening and requires medical care.

6 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. National Academy of Sports Medicine. Lactic acid build up in muscles: what you can do about it.

  2. Kaiser Permanente. Lactic acid test.

  3. MedlinePlus. Lactic acid test.

  4. 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

  5. Melbourne Sports Physiotherapy. What is lactic acid and how can it impact performance?

  6. MedlinePlus. Lactic acid test.

By Heather Jones
Heather M. Jones is a freelance writer with a strong focus on health, parenting, disability, and feminism.