What is it?
Sodium lactate is the sodium salt of lactic acid. It occurs naturally in the skin as part of the skin’s NMF (Natural Moisturizing Factors), and is an excellent humectant. It is a significantly stronger humectant than vegetable glycerin, with over twice the water holding capability.
INCI
Sodium lactate
Appearance
It is available as a power or a thin liquid that is typically a solution of approximately 60% strength.
Usage rate
0.5–5% (the numbers I’ve found vary quite widely—I’ve seen up to 10%)
Scent
None
pH
7.5–9
Solubility
Water
Why do we use it in formulations?
In skin care products it it used primarily as a humectant. It is second only to hyaluronic acid in its ability to hold water! It can also reduce tackiness in formulas, and is a keratolytic. Sodium lactate increases skin hydration in both leave-on and rinse-off applications.
It can also be used as a pH adjustor and buffering agent.
In bar soaps it can be included to harden the bar faster and improve un-moulding, though it can also accelerate trace.
It is sometimes sold as a preservative, but it is absolutely not a preservative. It can help boost preservative function, but it is not a preservative on its own.
Do you need it?
No, but if you have dry skin I’d highly recommend it. It’s inexpensive and versatile.
Strengths
Non-sticky, highly effective humectant.
Weaknesses
Sodium lactate is rich in electrolytes, so it doesn’t play well with electrolyte-sensitive emulsifiers and thickeners.
Alternatives & Substitutions
Other humectants would be a good place to start; vegetable glycerine, propanediol, and sodium PCA would all be good choices. Watch for the stickiness factor, though! If a recipe already contains some glycerine, replacing sodium lactate with even more glycerine could make the end product stickier than intended.
Sodium lactate and lactic acid are never interchangeable.
How to Work with It
Include it in the water phase. I’ve found conflicting information about its heat stability; if you’re using a 5% or less it could easily be moved from the heated water phase to the cool down phase, but if you’re using enough that your cool down phase would be larger than 10% of the recipe that could destabilize your emulsion.
I usually use the 60% liquid solution version of sodium lactate in my formulations. If you have the powdered version you’ll want to use 60% of the amount and make up the remaining 40% with distilled water. For example, if a formulation called for 10% sodium lactate solution you would use 6% sodium lactate powder and 4% distilled water.
Storage & Shelf Life
Stored somewhere cool, dark, and dry, sodium lactate should last for at least 5–6 years.
Tips, Tricks, and Quirks
I’ve read the sodium lactate can make skin sun-sensitive above 2.5%, but have not been able to find any additional sources for that claim. No suppliers warn of sun sensitivity while commonly recommending higher usage levels.
Recommended starter amount
100mL
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