Lactic acid

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What is it? Lactic acid is an alpha hydroxy acid that is used for pH adjusting and for creating skincare formulations that chemically exfoliate the skin. Humans have been embracing lactic acid in skincare for centuries—lactic acid is part of the magic of a milk bath! Lactic acid is considered to be more gentle than its sister AHA, glycolic acid.

Health Canada regulations stipulate that all formulations that contain 3% or more lactic acid must bear these warnings:

  • “Use only as directed.”,
  • “Avoid contact with the eyes.”,
  • “If irritation persists, discontinue use and consult a physician.”,
  • “It is recommended that prior to exposure to the sun, users cover areas where AHAs have been applied with sunscreen.”,
  • “Contact of the product with the skin must be of limited frequency or duration.”

Lactic acid is part of the skin’s natural moisturizing factor (NMF), compromising 10–12%.
INCI Lactic acid
Appearance It is often sold as an 88% or 90% liquid solution; this is is a clear, slightly viscous fluid.
Usage rate For pH adjusting, generally less than 1% (though usually less than 0.5%). For chemical exfoliation, no more than 10%, though I’d recommend starting with less.

Health Canada regulations limit non-professional use of lactic acid to 10%, with a pH equal to or greater than 3.5. Any concentrations higher than 10% are limited to professional use.

“The CIR Expert Panel evaluated the scientific data and concluded that … Lactic Acid… [was] safe for use in cosmetics and personal care products at concentrations of 10% or less, at final formulation pH of 3.5 or greater, when formulated to avoid increasing sun sensitivity or when directions for use include the daily use of sun protection.” (Source)
Scent Sour, tangy
pH 0.6
Solubility Lactic acid is water soluble.
Why do we use it in formulations? Lactic acid lowers the pH of our formulations; it is often used at very low concentrations to adjust pH.

In higher concentrations lactic acid acts as a chemical exfoliant and skin care active.

Some skincare benefits from using lactic acid include:
Do you need it? No, but it is very useful if you are interested in making high-performance skin care.
Refined or unrefined? The lactic acid used in cosmetics and skin care is always a refined product.
Strengths Potent pH adjustor, occurs naturally in the skin, mild as far as acids go.
Weaknesses Like all potent ingredients, it requires care when formulating with it.
Alternatives & Substitutions Other pure acids (citric acid is typically the most readily available) will work for pH adjusting, though it won’t be a 1-for-1 swap; you’ll need to test and adjust the formulation using the new acid.

Other alpha hydroxy acids like mandelic acid and glycolic acid can also be used to create exfoliating products. As with pH adjusting, this will not be a 1-for-1 swap; you will need to test and adjust the pH of the formulation to ensure it is safe.
How to Work with It Wear gloves; concentrated lactic acid is very acidic.

I’d say you need a digital pH meter to formulate products where lactic acid is a feature ingredient. The precise pH of the formulation is very important for safety, and strips aren’t very precise.

Lactic acid can be hot or cold processed.

Ensure the final pH of the product is 3.5 or greater: if you are creating an exfoliating product you will almost certainly need to raise the pH of your formulation (I use a 10% sodium hydroxide solution). As lactic acid has a pKa of 3.86, I recommend aiming for a pH close to 3.86 for optimal performance. Learn more about pKa with this fabulous article from Lab Muffin!

If following a formulation that calls for lactic acid, make sure you pay attention to the concentration called for in the formulation. If yours is a different concentration, adjust the lactic acid and water content of the formulation if required to end up with the same final percentage of lactic acid.
Storage & Shelf Life Stored somewhere cool, dark, and dry, lactic acid should last at least 2 years.
Tips, Tricks, and Quirks I recommend re-packaging your lactic acid in a glass bottle with a dropper top lid for easy dispensing.

You can create a buffer with lactic acid and sodium lactate in a 1:2 ratio, which should hold a formulation around a pH of 4. Learn more here.

Lactic acid does occur in milk, but cosmetic grade lactic acid is synthesized (and vegan).

Do not use lactic acid (or other AHAs) together with retinol. Do not apply to irritated skin.
Recommended starter amount 30mL (1fl oz) for pH adjusting; 60mL if you intend to use it as a chemical exfoliant.
Where to Buy it  Buy it from an online DIY ingredient supplier or Amazon.

Some Formulations that Use Lactic acid

Skills

Posted on

June 30, 2022