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

Other gentle exfoliants like lactic acid and azelaic acid can get rid of dead skin cells that might clog pores while improving your skin’s tone and texture. —Jessica Kasparian, SELF, 18 Apr. 2025

Glycolic acid and lactic acid are AHAs (alpha-hydroxy acids) that promote an even complexion, reduce hyperpigmentation and soften fine lines. —Caroline C. Boyle, USA Today, 2 Apr. 2025

Textured Skin: Exfoliating ingredients like lactic acid, salicylic acid, and urea can all help smooth out textured skin, says Dr. Ibrahim. —Deanna Pai, Vogue, 14 Feb. 2025

AHAs like mandelic or lactic acids gently exfoliate to buff away dead skin cells that might make your lips feel flaky or rough. —Jessica Kasparian, SELF, 18 Mar. 2025

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