lactic acid

noun

: a hygroscopic organic acid C₃H₆O₃ present normally especially in muscle tissue as a by-product of anaerobic glycolysis, produced in carbohydrate matter usually by bacterial fermentation, and used especially in food and medicine and in industry

Examples of lactic acid in a Sentence

Recent Examples on the Web

The mask also contains glycolic and lactic acids to fade hyperpigmentation and remove dead skin cells. —Kyra Surgent, InStyle, 28 May 2026

Both cottage cheese and farmer’s cheese are made from combining milk with lactic acid-producing bacteria. —Sarah Bence, Verywell Health, 24 May 2026

As more lactic acid forms, the milk becomes more acidic, the flavor turns tangy, and the texture begins to shift. —Samantha Agate, Miami Herald, 23 May 2026

As the bacteria produce lactic acid, the milk becomes more acidic, which causes its proteins — called casein — to stop floating freely and link together into a microscopic network. —Samantha Agate, Charlotte Observer, 23 May 2026

Word History

First Known Use

1790, in the meaning defined above

Rhymes for lactic acid

• antacid
• placid

Kids Definition

lactic acid

noun

lac·​tic acid

ˌlak-tik-

: an organic acid present especially in muscle tissue as a result of the breakdown of carbohydrates (as glycogen), is made from carbohydrates usually by fermentation by bacteria, and is used especially in food and medicine

Medical Definition

lactic acid

noun

: a hygroscopic organic acid C₃H₆O₃ that is known in three optically isomeric forms:

a

or D-lactic acid

ˈdē- 

: the dextrorotatory form present normally in blood and muscle tissue as a product of the anaerobic metabolism of glucose and glycogen

b

or L-lactic acid

ˈel- 

: the levorotatory form obtained by biological fermentation of sucrose

c

or DL-lactic acid

ˈdē-ˈel- 

: the racemic form present in food products and made usually by bacterial fermentation (as of whey or raw sugar) but also synthetically, and used chiefly in foods and beverages, in medicine, in tanning and dyeing, and in making esters for use as solvents and plasticizers