Lactic Acid

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A popular alpha hydroxy acid (AHA), lactic acid can be naturally extracted from milk, but is usually synthesized in a lab for use in cosmetics in order to ensure its purity. Lactic acid’s smoothing abilities are similar to that of glycolic acid.

Lactic Acid (Wikipedia)
Lactic acid
Skeletal formula of L-lactic acid
L-Lactic acid
Ball-and-stick model of L-lactic acid
Racemic lactic acid sample.jpg
DL-Lactic acid
IUPAC name
2-Hydroxypropanoic acid
Other names
Milk acid
50-21-5 YesY
79-33-4 (L) YesY
10326-41-7 (D) YesY
ChEMBL ChEMBL330546 YesY
ChemSpider 96860 YesY
Jmol 3D image Interactive graph
Molar mass 90.07948
Melting point L: 53 °C
D: 53 °C
D/L: 16.8 °C
Boiling point 122 °C (252 °F; 395 K) @ 12 mmHg
Acidity (pKa) 3.86, 15.1
1361.9 kJ/mol, 325.5 kcal/mol, 15.1 kJ/g, 3.61 kcal/g
G01AD01 (WHO) QP53AG02
GHS pictograms GHS-pictogram-acid.svg
H315, H318
P280, P305+351+338
Related compounds
Other anions
acetic acid
glycolic acid
propionic acid
3-hydroxypropanoic acid
malonic acid
butyric acid
hydroxybutyric acid
Related compounds
sodium lactate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YesYN ?)
Infobox references

Lactic acid is an organic compound with the formula CH3CH(OH)CO2H. It is a white, water-soluble solid or clear liquid that is produced both naturally and synthetically. With a hydroxyl group adjacent to the carboxyl group, lactic acid is classified as an alpha hydroxy acid (AHA). In the form of its conjugate base called lactate, it plays a role in several biochemical processes.

In solution, it can ionize a proton from the carboxyl group, producing the lactate ion CH3CH(OH)CO2. Compared to acetic acid, its pKa is 1 unit less, meaning lactic acid deprotonates ten times more easily than acetic acid does. This higher acidity is the consequence of the intramolecular hydrogen bonding between the α-hydroxyl and the carboxylate group.

Lactic acid is chiral, consisting of two optical isomers. One is known as L-(+)-lactic acid or (S)-lactic acid and the other, its mirror image, is D-(−)-lactic acid or (R)-lactic acid. A mixture of the two in equal amounts is called DL-lactic acid.

Lactic acid is hygroscopic. DL-lactic acid is miscible with water and with ethanol above its melting point which is around 17 or 18 °C. D-lactic acid and L-lactic acid have a higher melting point.

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 and as high as 25 mmol/L afterward.

In industry, lactic acid fermentation is performed by lactic acid bacteria, which convert simple carbohydrates such as glucose, sucrose, or galactose to lactic acid. These bacteria can also grow in the mouth; the acid they produce is responsible for the tooth decay known as caries.

In medicine, lactate is one of the main components of lactated Ringer's solution and Hartmann's solution. These intravenous fluids consist of sodium and potassium cations along with lactate and chloride anions in solution with distilled water, generally in concentrations isotonic with human blood. It is most commonly used for fluid resuscitation after blood loss due to trauma, surgery, or burn injury.

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