Sodium benzoate

Sodium benzoate is the sodium salt of benzoic acid; it is “produced by the neutralization of benzoic acid with sodium bicarbonate, sodium carbonate, or sodium hydroxide” (source). Benzoic acid is a naturally occurring compound that can be found in foods like cranberries (source).

When sodium benzoate is dissolved in water, a portion of it converts to benzoic acid—the active, anti-microbial form of the ingredient. Just how much active benzoic acid (and therefore anti-microbial action) is present in your formulation depends on the pH of the formulation. It is most active at pH 3 (~94% active), but that’s much more acidic than we want our skincare products to be. Its activity decreases sharply as the pH raises; it is just 1.55% active at pH 6 (source) and 0% active at pH 7 (source).

Sodium benzoate has GRAS (“generally recognized as safe”) status with the FDA as a food substance. It is a common food industry preservative, and is also used as as preservative ingredient in cosmetics; primarily as an anti-fungal.

Sodium benzoate

White solid; mine is small spherical granules that are ~3mm across.

• 0.2–0.5% (Cosroma, Chemists Corner/Perry Romanowski)
• “The usual doses of use usually vary between 0.8 and 2.0%. At pH above 5.5, the dosages could be significantly higher.” (Chemipol)
• Up to 1% (Lotion Crafter)
• The CIR reports usage ranging from 0.000001–1% in commercial products

Nothing noticeable

8.0–9.0

Sodium benzoate is more effective at lower pHs; I’d aim for 4.5–5. Lotion Crafter notes benzoic acid is inactivated by non-ionics, but I’ve found quite a few commercial products that use it alongside non-ionics like polysorbate 60, PEG-100 stearate, and PEG-32, so I expect there’s a good dose of “it depends” here. Harry’s Cosmeticology notes benzoic acid as a “preservative that appears to be much less affected by the presence of non-ionic surfactants” when compared to propylparaben and methylparaben.

From Harry’s Cosmeticology: “its antimicrobial action is strongly pH-dependent so that approximately 60 times as much benzoic acid is required at pH 6 as at pH 3.”

Water soluble, though the granules I have are quite slow to dissolve.

Sodium benzoate is included in formulations for its anti-microbial benefits. It is “primarily an anti-fungal” and has “poor activity against pseudomonads”. It should not be used as a stand alone preservative.

No, but if you’re a more experienced formulator who is interested in experimenting with natural preservatives it can be a good addition to your DIY pantry.

Sodium benzoate only exists as a refined ingredient.

Natural, inexpensive preservative ingredient.

As it requires a low pH to work, sodium benzoate is not suitable for preservative use in higher pH products. Personally, I would not rely on it as an element of my preservation system in formulations with a pH above 5.

Please read this FAQ.

Add sodium benzoate in the post-heat phase (as demonstrated by Lotion Crafter here) or cool down phase.

Test and adjust the pH of the formulation to a pH of 4.5–5. I find sodium benzoate pulls the pH of formulations up a bit, requiring the addition of an acid to lower it to the effective range.

Inclusion of a chelator is recommended.

Stored somewhere cool, dark, and dry, sodium benzoate should last at least 2 years after its manufacture date.

Sodium benzoate is also part of Geogard Ultra™ (22–28%).

A blend of sodium benzoate and potassium sorbate is a common preservative system in hydrous ingredients like botanical extracts and liquid hydrolyzed proteins.

It is possible for sodium benzoate/benzoic acid to break down into benzene when it is combined with L-ascorbic acid. This reaction is exacerbated by UV exposure. This is discussed on page 14 of this CIR document, mostly in the context of canned sodas.

“There is some concern that Sodium Benzoate in combination with L-Ascorbic Acid in products can form Benzene, a known human carcinogen. The presence of ascorbic acid and benzoates alone does not lead to the formation of benzene. Certain additional conditions are required for trace levels of benzene to form, including heat, ultraviolet light and metallic ions in the mixture. Therefore, a product containing ascorbic acid and benzoates will not necessarily contain any detectable levels of benzene. The use of EDTA, which chelates metallic ions can therefore be of assistance in the inhibition of benzene formation. Citric Acid is not thought to induce significant benzene production in combination with Benzoic Acid, but some evidence suggests that in the presence of ascorbic acid and benzoic acid, citric acid may accelerate the production of benzene. Therefore, the use of Sodium Benzoate and L-Ascorbic Acid and Citric Acid in the same cosmetic formulations should be avoided.” – Lotion Crafter

30g (1.06oz)

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