These bacteria can also grow in the mouth; the acid they produce is responsible for the tooth decay known as cavities.

Lactic acid is produced in human tissues when the demand for oxygen is limited by the supply.

This occurs during tissue ischemia when the flow of blood is limited as in sepsis or hemorrhagic shock.

[16] Swedish chemist Carl Wilhelm Scheele was the first person to isolate lactic acid in 1780 from sour milk.

[17] The name reflects the lact- combining form derived from the Latin word lac, meaning "milk".

[citation needed] In 2006, global production of lactic acid reached 275,000 tonnes with an average annual growth of 10%.

[19] Lactic acid is produced industrially by bacterial fermentation of carbohydrates, or by chemical synthesis from acetaldehyde.

[23] Racemic lactic acid is synthesized industrially by reacting acetaldehyde with hydrogen cyanide and hydrolysing the resultant lactonitrile.

[24] Synthesis of both racemic and enantiopure lactic acids is also possible from other starting materials (vinyl acetate, glycerol, etc.)

During intense exercise, the respiratory chain cannot keep up with the amount of hydrogen ions that join to form NADH, and cannot regenerate NAD+ quickly enough, so pyruvate is converted to lactate to allow energy production by glycolysis to continue.

Lactate serves as a metabolic fuel being produced and oxidatively disposed in resting and exercising muscle and other tissues.

[29] Some evidence suggests that lactate is important at early stages of development for brain metabolism in prenatal and early postnatal subjects, with lactate at these stages having higher concentrations in body liquids, and being utilized by the brain preferentially over glucose.

[17] Blood tests for lactate are performed to determine the status of the acid base homeostasis in the body.

During childbirth, lactate levels in the fetus can be quantified by fetal scalp blood testing.

In the presence of catalysts lactide polymerize to either atactic or syndiotactic polylactide (PLA), which are biodegradable polyesters.

Lactic acid is also employed in pharmaceutical technology to produce water-soluble lactates from otherwise-insoluble active ingredients.

Lactic acid containing bacteria have shown promise in reducing oxaluria with its descaling properties on calcium compounds.

[41] Lactic acid is found primarily in sour milk products, such as kumis, laban, yogurt, kefir, and some cottage cheeses.

Other sour styles of beer include Berliner weisse, Flanders red and American wild ale.

[52] Lactic acid is produced commercially by fermentation of carbohydrates such as glucose, sucrose, or lactose, or by chemical synthesis.

[54] Lactic acid is used in some liquid cleaners as a descaling agent for removing hard water deposits such as calcium carbonate.