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What is Lactic Acid?

By J. MacArthur
Updated Mar 03, 2024
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Lactic acid, also known as 2-hydroxypropanoic or milk acid, is a compound formed when glucose is broken down under certain conditions in a living creature or by some types of bacteria. In a person, for example, it is an important part of producing energy for strenuous exercise and helps with certain liver functions. During extremely intense exercise, it can buildup to excess and cause short-term burning sensations in muscles. This acid can also be found in certain dairy products, such as yogurt, as well as sourdough breads and some beers and wines as a result of fermentation.

Production and Use in the Body

Skeletal muscles and other tissues commonly produce lactic acid, even while at rest. The body creates this acid as it breaks down carbohydrates to produce energy. The acid only becomes an issue when there are unusually large amounts of it.

This can happen when there is not enough oxygen in the body to completely break down glucose during physical activity. Energy in a person's body is typically created with the assistance of oxygen during aerobic exercise. When oxygen levels reach their limit, but more energy is needed, then the activity becomes anaerobic, which means that energy needs to be produced through other methods. Through a complex process known as glycolysis, glycogen in the muscles breaks down into glucose and then into pyruvate or pyruvic acid.

During aerobic exercise, the pyruvate undergoes an oxidation process that helps remove it. When someone participates in strenuous, anaerobic exercise, however, his or her body does not have the oxygen available to do this. Under these conditions, the excess pyruvate produces lactic acid, which helps generate short-term bursts of energy. A "fight-or-flight" response, for example, often relies on this acid for the energy a person needs to quickly run at high speeds.

Use By The Liver

One common use for lactic acid in a human body is the formation of glucose. Moderate amounts of this acid can move through someone's blood stream and reach the liver, where it undergoes a process called gluconeogenesis to become glucose. This is then either used to maintain healthy glycogen levels within the liver or passed back into the body for use as blood-sugar.

Extreme Activity

During prolonged strenuous activity, the high amounts of lactic acid may produce hydrogen ions that cause burning sensations in muscles. This is typically quite painful, and many serious athletes and bodybuilders experience this discomfort during intense exercise or weightlifting. The pain is fairly brief, however, and helps prevent serious injury since it usually makes the person stop using a certain muscle group.

Common Myths

A widespread belief among some people is that ongoing muscle soreness following an intense workout is due to a buildup of lactic acid. In truth, most research indicates that only immediate soreness or burning sensations result from too much of this compound. Minuscule tears and inflammation in the muscles usually cause soreness and fatigue that last for several days. Proper training and exercise, including warming up and cooling down muscles, adequate stretching, and a healthy, high-carbohydrate diet, can help prevent injury.

Potential Health Concerns

Very high levels of lactic acid can cause a serious, sometimes life-threatening condition called lactic acidosis. Symptoms of this condition include rapid breathing, sweating, and nausea and vomiting. Healthcare professionals typically draw a blood sample to check acid levels when they suspect a person might have this condition. While extreme over-exercising and overheating can result in lactic acidosis, it can also be caused by alcohol poisoning, liver disease, and a lack of oxygen, due to something like carbon monoxide poisoning.

Use In Food

A number of foods also include lactic acid to alter the pH balance or change the flavor. Certain types of bacteria added to milk, for example, produce the acid, which helps create the texture and tartness found in yogurt. Sourdough bread often relies on both yeast and bacteria in the air around the dough's starter for its tart flavor, usually caused by the formation of acid within the bread. Beer and wine sometimes include bacteria that produces this acid, which can help eliminate other, somewhat unpleasant flavors produced during fermentation.

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Discussion Comments

By anon153002 — On Feb 15, 2011

there is nothing inherently "non-vegan" about lactic acid, although my understanding is that most of the time when you see lactic acid on an ingredient label it comes from an animal (dairy) source. Many products will specifically state in the ingredients that the lactic acid in their product is from a vegetable source (usually sugar beets) if that is the case.

In the absence of any other markings on something advertising it being vegetarian or vegan, in some cases the only way to know for sure would be to contact the manufacturer and ask what the source of their lactic acid is.

Also some veg advocacy groups have lists of vegan items available in everyday grocery stores, so that might be worth checking out in case the thing you are unsure about it on one of them.

By anon151959 — On Feb 12, 2011

Can a vegan consume foods with lactic acid? maxu

By treme2005 — On Jul 22, 2010

Lactic acid is added to fizzy sodas and some fruit juices to regulate acidity. Lactic acid can extend the shelf life in meats, poultry, and fish by controlling pathogenic bacteria in these food items.

Lactic acid is also added to candies like gummy bears, hard candy, and other confectionary products to reduce stickiness, improve quality, add a hint of acidic flavor, and maintain a longer shelf life.

By skinnylove — On Jul 22, 2010

Lactic acid occurs naturally in some food. Natural fermentation creates lactic acid in in cheese, soy sauce, sourdough, meat products, and pickled vegetables.

Lactic acid is also used as a pH regulator or a preservative. Lactic acid can sometimes be used as a flavoring agent.

By jsw23 — On Jul 22, 2010

The process of lactic acid removal takes approximately one hour, but this can be accelerated by performing an appropriate cool down. A good cool down ensures a rapid and continuous supply of oxygen to the muscles.

By PurpleSpark — On Jul 21, 2010

Lactic acid helps to keep the skin at acid pH levels, limiting the growth of bacteria. It is known to have good results with skin conditions as diverse as wrinkles and acne. It is also very good to use on other parts of the body where tough skin develops, such as elbows and heels.

By dega2010 — On Jul 21, 2010

Lactic acid is a largely used hydroxyl acid derived from sour milk. As it doesn’t sound very appealing, it is very popular in skin care use. It is said that Cleopatra bathed in soured milk to pamper her skin.

As we get older our skin loses its ability to shed dead skin cells. This increases our need to exfoliate. Lactic acid is a great exfoliant. It helps to peel away layers of dead skin and leaves us with a healthy glow.

By mutsy — On Jul 17, 2010

Great article- I wanted to add that lactic acidosis can be caused by alcohol, cancer, exercising too intensely, liver failure, low blood sugar, heart failure, severe anemia and seizures.

Doctors will usually perform a urine PH test along with a serum electrolyte test to confirm the acidosis diagnosis.

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