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Lactic acid (Molecule of the Month for January 2008)

Milk Acid, AHA

Lactic acid, also known as milk acid, is a chemical compound that plays a role in several biochemical processes. It was first isolated in 1780 by a Swedish chemist, Carl Wilhelm Scheele, and is a carboxylic acid with a chemical formula of H]C3H5O3. It has a hydroxyl group adjacent to the carboxyl group, making it an alpha hydroxy acid (AHA). Lactic acid is primarily found in sour milk products, such as: koumiss, leban, yogurt, kefir and some cottage cheeses. The casein in fermented milk is coagulated (curdled) by lactic acid.

In solution, it can lose a proton from the acidic group, producing the lactate ion CH3CH(OH)COO−. In animals, L-lactate is constantly produced from pyruvate via the enzyme lactate dehydrogenase (LDH) in a process of fermentation during normal metabolism and exercise. It does not increase in concentration until the rate of lactate production exceeds the rate of lactate removal which is governed by a number of factors including: monocarboxylate transporters, concentration and isoform of LDH and oxidative capacity of tissues. The concentration of blood lactate is usually 1-2 mmol/L at rest, but can rise to over 20 mmol/L during intense exertion. Contrary to popular belief, this increased concentration of lactate does not directly cause acidosis, nor is it responsible for delayed onset muscle soreness. This is because lactate itself is not capable of releasing a proton, and secondly, the acidic form of lactate, lactic acid, cannot be formed under normal circumstances in human tissues. Analysis of the glycolytic pathway in humans indicates that there are not enough hydrogen ions present in the glycolytic intermediates to produce lactic or any other acid.

A much weaker acid than glycolic acid, lactic acid is best known as an acid peel for the removal of sun spots, hyperpigmentation, liver spots and other skin discolorations. A lactic acid peel is also recommended for the reduction of Rosacea as it is the mildest of AHA peels.

Formal Chemical Name (IUPAC)
(S)-2-hydroxypropanoic acid



Picture of Lactic acid 3D model

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Lactic acid structure
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Picture of Lactic acid

C3 H6 O3

Update by Karl Harrison
(Molecule of the Month for January 2008 )

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