Lactic acid

• BPLactic Acid
• JPLactic Acid
• Ph. Eur.Lactic Acid
• USP–NFLactic Acid

Acidum lacticum; 2-hydroxypropanoic acid; α-hydroxypropionic acid; DL-lactic acid; milk acid; Purac; E270

2-Hydroxypropanoic acid · [50-21-5]

UNII 3B8D35Y7S4 · PubChem CID 612

C3H6O3 · 90.08

pH adjuster, buffering agent

Typical concentrations: — · Dosage forms: Liquid, Semi-solid, Sterile (parenteral/ophthalmic)

Used as an acidulant and to adjust pH in oral, topical, vaginal and parenteral products, and, with sodium lactate, as a buffer. It is used in topical preparations as a humectant and, at higher concentrations, as a keratolytic and exfoliating agent (an alpha-hydroxy acid). It is widely used in foods as an acidulant and preservative.

A practically odourless, colourless or slightly yellow, viscous, hygroscopic liquid with an acid taste. Pharmacopoeial lactic acid contains about 88–92% w/w of C3H6O3 as a mixture of lactic acid and its condensation products (lactoyllactic acid and polylactic acids) in equilibrium with water. It is usually racemic; (S)-lactic acid has its own monograph.

Content

88–92% w/w

pKa

≈ 3.86 at 25 °C

Density

≈ 1.21 g/cm³ at 20 °C

Solubility

miscible with water, ethanol and ether

Hygroscopic. When concentrated, especially on heating, it condenses to lactoyllactic acid and lactide, which hydrolyse back to lactic acid on dilution and warming. Store in a well-closed container in a cool, dry place.

Incompatible with oxidising agents, iodides and albumin. Reacts with alkalis and with carbonates, releasing carbon dioxide.

Produced mainly by fermentation of carbohydrates such as glucose, sucrose or lactose with lactic acid bacteria, followed by purification; it can also be synthesised from acetaldehyde and hydrogen cyanide via lactonitrile.

A normal product of human metabolism, regarded as non-toxic in dilute form. The concentrated acid is corrosive and irritant to skin, eyes and mucous membranes; topical products with high concentrations may cause stinging and irritation.

Wear gloves, eye protection and protective clothing when handling the concentrated acid, and work with adequate ventilation.

GRAS listed. Accepted as a food additive in Europe (E270). Included in the FDA Inactive Ingredient Database (intravenous, intramuscular and subcutaneous injections; oral, topical and vaginal preparations) and in parenteral and non-parenteral medicines licensed in Europe.

(S)-Lactic acid; sodium lactate; calcium lactate; glycolic acid.

Because commercial lactic acid contains condensed forms, solutions should be diluted and allowed to stand (or warmed) before titration or final pH adjustment so that the equilibrium is reached. Lactic acid is also the monomer for poly(lactic acid) and poly(lactic-co-glycolic acid) biodegradable polymers.