Lactic Acid

Lactic acid is fuel for your cells during intense exercise. It’s created when your body breaks down glucose and other carbohydrates. It’s a common myth that muscle soreness you feel after exercise is caused by lactic acid trapped in your cells. Studies have found that’s not true.


An illustration of a lactic acid molecule in a soccer player's muscle fibers
The temporary rise in lactic acid caused by intense physical activity isn’t dangerous and usually won’t cause any symptoms.

What is lactic acid?

Lactic acid is a chemical your body produces when your cells break down carbohydrates for energy. You might see it referred to as lactate. Muscle cells and red blood cells make the most lactic acid, but it can come from any tissue in your body.

Most people think of lactic acid in their muscles during a tough workout. Your muscles do produce lots of lactic acid when you’re exercising, but that’s not the only activity that can create it. Anything that makes your body use more oxygen than usual can cause your cells to produce lactic acid.

A workout, doing yardwork or lugging heavy boxes while you’re helping a friend move can all cause a short-term increase in lactic acid in your body. That temporary rise in lactic acid isn’t dangerous and usually won’t cause any symptoms. Your liver and kidneys filter lactic acid out of your blood and break it down into glucose (blood sugar).


Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy


What does lactic acid do?

Your body usually fuels your muscles with oxygen (aerobically). If you start doing intense physical activity faster than your body can get oxygen to your muscles and other tissues, your cells break down glucose to create the energy you need to keep moving (anaerobically). Lactic acid is created when you’re generating energy anaerobically.

Lactic acid has three main functions, including:

  • Energy: Your body makes lactic acid to fuel cells when they’re working harder than usual.
  • Generating glucose (gluconeogenesis): Your liver and kidneys filter lactic acid out of your blood after it’s created in other tissue. They break it down and convert it into new glucose that your body can use for energy in the future.
  • Molecular signaling: Lactic acid in your blood is a signal molecule throughout your body. Think of it like a set of flags or markers a construction crew puts down before they begin working in an area. Lactic acid attracts cells in your immune system to heal wounds and fight infections.

Does lactic acid make your muscles burn?

It’s a common myth that lactic acid makes your muscles ache or burn after a workout. Experts used to think a buildup in lactic acid caused some of the soreness you feel in the days after intense activity. But studies have found that lactic acid is flushed out of your muscles so quickly that it doesn’t damage your cells or cause pain.

Usually, the soreness you feel in the days after a workout is caused by microtears (tiny tears in your muscle fibers). This can be a good thing — repairing these microtears makes muscles grow bigger and stronger. But if you’re experience severe muscle pain, you might have an injury like a pulled muscle (a muscle strain).


Where is lactic acid located in my body?

The organs and tissues that produce the most lactic acid include your:


Conditions and Disorders

What is a high lactic acid level?

Health conditions and infections that make it harder for your body to get fresh oxygen to your cells can raise your lactic acid levels. This can lead to lactic acidosis — a dangerously high lactic acid level. Lactic acidosis is a serious health condition that can be fatal.

Lactic acidosis is usually a complication of other health conditions, including:

The most common symptoms of lactic acidosis include:

If you have lactic acidosis, your body can’t process lactic acid fast enough and it starts to damage your organs and tissue. You might vomit as your body tries to remove extra lactic acid as fast as possible.

You can develop lactic acidosis if you push your body beyond its usual limits during a sport, workout or any type of intense physical activity. Working out and playing sports can safely test the limits of your endurance, but don’t “play through pain” or force yourself to keep moving when you’re physically exhausted.

Lactic acidosis is different than the temporary rise in your lactic acid level after a workout. Typically, your lactic acid level will return to its usual level as soon as you stop an intense physical activity. Your liver and kidneys start breaking the extra lactic acid down right away before you experience symptoms or complications.

What is a lactic acid level test?

A lactic acid level test is a blood test. A healthcare provider will test your lactic acid level if they think you might have lactic acidosis. Your provider will send a sample of your blood to a lab. The lab will check how much lactic acid is in your blood.

Having high lactic acid doesn’t automatically mean you have one of the serious conditions that causes lactic acidosis, but it’s usually a sign that your cells aren’t getting enough oxygen. Your provider will tell you what your results mean and which treatments you’ll need to lower your lactic acid level.

Lactate threshold testing for athletes

Some athletes perform a physical test called a lactate threshold test. Athletes use lactate threshold tests to understand the upper limits of their endurance so they can safely train or perform at their highest for as long as possible.

During a lactate threshold test, you’ll perform increasingly strenuous exercise while a healthcare provider monitors the level of lactic acid in your blood. They’ll take blood samples from you at set points throughout the test to check the lactic acid in your blood in real time.

Never intentionally workout until you’re exhausted. Lactate threshold tests must be done under a provider’s supervision to make sure you’re safe. Talk to your provider if you’re interested in a lactate threshold test as part of your training or exercise.



How can I take care of my muscles?

Lactic acid doesn’t cause pain in your muscles. It also doesn’t cause injuries.

In general, make sure to stretch and warm up before starting any intense physical activity. Increasing your overall flexibility will help prevent muscle injuries. The more you work your muscles by gradually stretching them, the more flexibility and give they have when you move.

Additional Common Questions

Is lactic acid a birth control?

A healthcare provider might prescribe you lactic acid combined with citric acid and potassium bitartrate as birth control. This is a vaginal gel that’s specifically formulated to prevent pregnancy when a person applies it into their vagina before having vaginal intercourse.

This medicine is different than the lactic acid that your body naturally produces. The typical, healthy amount of lactic acid in your body isn’t a form of birth control. It won’t affect your ability to get pregnant.

A note from Cleveland Clinic

Lactic acid has a bad reputation. Most people think it’s a painful side effect of working out that leaves your muscles aching and burning. In fact, the opposite is true. Your body uses lactic acid as a fuel source and to signal where you need healing.

Even though it’s not caused by overusing your muscles, lactic acidosis is a serious complication caused by other health conditions. Talk to your provider about how you can avoid it and which symptoms to watch out for.

Medically Reviewed

Last reviewed on 12/09/2022.

Learn more about our editorial process.

Appointments 216.444.2606