Natural Preservative Systems And pH: How To Keep “Clean” Beauty Formulas Truly Safe

Let’s stir up some magic in the lab with today’s hot topic: how to choose and use natural preservative systems so they actually work in real cosmetic formulas, not just on paper.

Every week I speak to founders who say “the natural preservative failed” when they tried to preserve a cleanser, toner or moisturiser. In the vast majority of cases, the problem is not that the natural preservative system is weak. The problem is that the pH, vehicle and synergy pieces were not designed together.

In this article, we will walk through five of the most common natural-leaning preservative systems, the pH windows they need, what formats they suit best, and how to adjust and buffer pH so your products pass real preservation challenge tests without sacrificing skin feel or your brand’s “clean beauty” identity.

I will also point out where glycols, chelators and packaging help make your natural preservative system more robust.

Why pH Makes Or Breaks Natural Preservative Systems

Weak-acid preservative systems only work when enough of the acid is present in its unionised form in the water phase. That balance between acid and salt is pH dependent, which is why so many natural systems insist on “effective below pH 5.5” in the technical data.

You can model this with the Henderson–Hasselbalch equation, but practically speaking it means:

If the finished pH sits only slightly above the pKa of the acid, a useful amount of the active acid is present.
If the pH drifts too high, you are essentially adding inactive salts and hoping for the best.

For example, benzoic acid has a pKa around 4.2. At pH 5.5 only a small fraction is unionised, which is why blends based on sodium benzoate work best when the formula is clearly on the acidic side. Sorbic acid, with a pKa around 4.8, keeps more active acid available at the same pH, so sorbate systems often look stronger than benzoate when you push toward pH 5.

On top of pH you also have:

Chelation to neutralise trace metals from botanicals, clays, pigments and process water that can destabilise preservatives and drive oxidation.
Water activity to control how much “free” water microbes can use, supported by humectants and solids.
Packaging to limit water ingress and back contamination in real bathroom use.

Once those foundations are in place, natural preservative systems behave much more predictably. I will now walk through five families that come up again and again in natural-leaning skincare and haircare.

System 1: Geogard BS (Sodium Benzoate & Potassium Sorbate)

INCI: Aqua, Sodium Benzoate, Potassium Sorbate

This is one of the most widely used “natural profile” preservative blends for clean beauty brands. It is water soluble, accepted by major natural and organic certification bodies, and can be used in both rinse-off and leave-on formulas.

Where this natural preservative shines

Acidic toners, essences and gel serums
Mild shampoos and body washes
Light emulsions and lotions for face and body

It offers broad-spectrum protection against bacteria, yeast and mould when used in the right pH range, typically from about pH 2 to 5.5, with better performance at the lower end of that range. Typical use rates are around 0.5 to 1.0 percent range, depending on product type and risk profile.

What this preservative system needs from you

Keep finished pH clearly acidic, ideally between 4.0 and 5.2 for leave-ons.
Add a biodegradable chelator such as sodium phytate or tetrasodium glutamate diacetate to bind iron and copper and sharpen preservative performance.
Support with a modest glycol stack (for example, glycerin plus propanediol or pentylene glycol) to lower water activity without wrecking skin feel.

Watch outs

If you push pH above 5.5 the active fraction of benzoic and sorbic acids collapses and the system may fail yeast and mould in challenge tests, even if bacteria look fine. Heavy botanical loads rich in proteins and sugars can adsorb part of the system, so always test in the final, fully loaded formula, not in a plain base. And think of coupling this preservative with another blend as well.

System 2: Dermosoft 1388 ECO (Sodium Levulinate & Sodium Anisate)

INCI (typical): Aqua, Glycerin, Sodium Levulinate, Sodium Anisate

This is a modern, plant-derived preservative pair based on levulinic acid and p-anisic acid, supplied as their sodium salts in a water–glycerin matrix. It is ECOCERT / COSMOS approved and popular in minimalist, sensitive-skin-friendly formulas.

Where this natural preservative system shines

Fragrance-free or fragrance-light hydrating serums and essences
Lamellar creams and lotions for sensitive skin
Gentle facial cleansers and micellar gels

It offers broad antimicrobial activity when used at the right concentration and pH. Supplier guidance typically suggests about 2.5 percent at pH 3.5, 3.5 percent at pH 4.5, 4 percent at pH 5.5 and up to 5 percent when you push toward pH 6.

What this system needs from you

Keep final pH usually between about 3.5 and 5.5, with the sweet spot often around 4.5 to 5.
Use it in the water phase and allow full dissolution; it is highly water soluble and can be heated to around 80 °C.
Add a chelator such as sodium phytate or GLDA in the water phase.
Support with a small amount of natural glycol (such as pentylene glycol) to reduce water activity and extend antimicrobial breadth.

Solubility and pH control in practice

You can add Dermosoft 1388 ECO directly to the water phase under stirring and heat that phase if needed. After emulsification and cooling, check pH at 25 °C and adjust gently:

Use lactic or citric acid solutions for downward corrections.
Use sodium hydroxide, sodium citrate or amino neutralisers such as arginine for upward corrections, depending on your brand stance.

If your system tends to drift, a low-level lactate or citrate buffer helps keep pH in the effective window over shelf life.

Watch outs

In formulas with very high botanical content, proteins and polysaccharides can interact with weak-acid systems. If your first challenge test is borderline on yeast, consider:

Nudging pH slightly lower within your skin comfort brief.
Adding a small sorbate component, if regulatory and label strategy allows.
Modestly increasing total Dermosoft 1388 ECO within supplier limits rather than jumping to an entirely different system.

System 3: Euxyl K 903 (Benzyl Alcohol, Benzoic Acid, Dehydroacetic Acid)

INCI: Benzyl Alcohol, Benzoic Acid, Dehydroacetic Acid, Tocopherol

Euxyl K 903 is a liquid preservative blend with broad-spectrum efficacy against bacteria, yeasts and moulds. It is suitable for many certified natural cosmetics and is particularly interesting because it also offers some vapour-phase activity, which helps in headspace and at the pump interface.

Where this natural preservative system shines

Face and body creams where you want a natural-leaning but robust preservative
Rinse-off and leave-on products positioned as “preservative conscious” rather than strictly preservative free
Products where you prefer to avoid sorbate odour but still want organic-acid support

The recommended pH range is around 3 to 6, with many formulators aiming for about 5 to 5.5 for skin comfort and efficacy.

Typical use levels for leave-ons are approximately 0.5 to 1.2 percent (ideally 1 percent), depending on product category and regulatory region.

What this preservative system needs from you

To get the best from Euxyl K 903 you should:

Formulate clearly in its effective pH range, ideally in the low to mid 5s.
Plan for a modest pH drop after addition, because the blend tends to lower pH by up to about 0.75 to 1.5 units in some systems.
Pre-disperse in a glycol or add into the cool-down water phase to ensure even distribution.
Include a chelator and, where appropriate, a small glycol stack for synergy.

Watch outs

Benzyl alcohol has a characteristic odour that some people perceive easily. If your formula is lightly fragranced or fragrance free, check that the smell is acceptable at the required use level.

Dehydroacetic acid and benzoic acid still depend on pH for activity. If the finished pH drifts above 6, efficacy falls and challenge tests may fail on yeast or mould, even if bacteria look good.

System 4: Rokonsal BSB-N (Benzyl Alcohol, Benzoic Acid, Sorbic Acid)

INCI: Benzyl Alcohol, Glycerin, Benzoic Acid, Sorbic Acid

This preservative blend combines benzyl alcohol with benzoic and sorbic acids and is widely marketed as a mild, broad-spectrum preservative suitable for natural cosmetics, including those following BDIH and similar guidelines.

Where this natural preservative system shines

Mild creams and lotions for face and body
Gentle cleansers and surfactant-based products
Emulsions and aqueous gels where you can keep pH comfortably acidic

It is effective against gram-positive and gram-negative bacteria, yeasts and moulds at acidic pH, and is typically used at about 0.5 to 1.0 percent (ideally 1 percent) when used as the sole preservative.

What this system needs from you

The key requirement is pH control. Rokonsal BSB-N is only considered active when the final product pH is below about 5.0 to 5.4, with supplier information clearly stating that it should not be used above this range.

In practice:

Aim for a finished pH of roughly 4.5 to 5.0.
Adjust pH with lactic acid or citric acid as needed, then verify at 25 °C after 24 to 48 hours.
Add Rokonsal in the cool-down phase and avoid heating the blend above about 80 °C, as high temperatures can reduce activity.

A chelator and a supportive glycol stack further improve robustness, particularly in high-botanical formulations.

Watch outs

The blend can have a characteristic odour. In some bases this is easily masked with fragrance; in very low-fragrance or fragrance-free formulas you should sensory test carefully at the required level.

If pH drifts above 5.4 during stability, the system loses efficacy and products risk microbial spoilage, so buffering is essential.

System 5: Leucidal SF Max (Lactobacillus Ferment)

INCI: Lactobacillus Ferment

Leucidal SF Max is a ferment-based ingredient produced by fermenting Lactobacillus in a plant-derived medium. It offers both antimicrobial and moisturising benefits and is marketed as a naturally derived, ECOCERT- and Whole Foods–approved option.

Where this natural preservative system shines

Leucidal SF Max is most useful as part of a broader natural preservation strategy in:

Hydrating creams and lotions where you want a moisturising “skin conditioning” story alongside antimicrobial support
Products where you want a fully ferment-based or probiotic-inspired narrative
Formulas that will be combined with organic acids or glycols as co-preservatives

It is active over a relatively wide pH range from about 3 to 8 and is typically used at 2 (when coupled) to 4 percent (when used alone).

What this system needs from you

To get reliable performance you should:

Use it in the water phase and add below about 70 °C.
Combine it with co-preservatives such as pentylene glycol (preservative booster at 5%), AMTicide Coconut or organic acid salts like potassium sorbate for broader and more reliable protection, especially against yeast and mould.
Keep pH within its active window (typically around 4 to 6 for most skin-facing products) and still include chelation and a sensible glycol stack.

Watch outs

Although suppliers publish challenge test data, independent experience shows that ferment-only systems can be variable in real-world, high-botanical, high-risk formulas. For anything beyond the lowest-risk formats I recommend treating Leucidal SF Max as a key part of a multi-hurdle strategy, not as a stand-alone preservative for complex, nutrient-rich emulsions.

How To Set And Hold pH For Natural Preservative Systems

Regardless of which natural preservative family you choose, the workflow to set and hold pH is similar.

Choose your preservative system first.
Decide whether your formula will be based on benzoate–sorbate, levulinate–anisate, benzyl alcohol–acid blends, ferment-based systems, or a combination. Set your target pH around the most restrictive component.
Make your batch and measure pH at 25 °C.
A hot pH reading is only a reference. Always cool a sample to 25 °C, stir gently and measure again before adjusting.
Adjust downwards with pre-made acid solutions (if too alkaline).
Use, for example, a 20 percent citric acid solution or a 10 percent lactic acid solution, dosing slowly under stirring. This prevents local pH shocks that can destabilise emulsions or thickeners.
Adjust upwards with controlled alkali or buffered solutions (if too acidic).
Use an 18 percent sodium hydroxide solution, or a sodium citrate solution, or an amino neutraliser such as arginine if that better fits your brand’s positioning. Start with very small additions and re-measure after each one.
Add a buffer if the system is drift-prone.
Low-level citrate or lactate buffers help maintain pH in the effective range for organic-acid-based systems through temperature cycling and early shelf life.
Re-check pH after relaxation and during stability.
Natural gums, clays and humectants can shift pH slightly as they fully hydrate and equilibrate. Always re-check after 24–48 hours and again at stability checkpoints.

This kind of pH discipline is what makes the difference between a natural preservative system that passes challenge testing once and one that remains reliable across batches and seasons.

Solubility, Order Of Addition And Synergy

Natural preservative systems are much easier to work with when you respect their preferred phase and support them with smart synergies.

Benzoate, sorbate, levulinate and anisate salts belong in the water phase and benefit from being fully dissolved before emulsification or surfactant thickening.
Benzyl alcohol usually behaves best when pre-dispersed in a glycol or added into the cool-down phase of an emulsion, before fragrance.
Leucidal SF Max belongs in the water phase during cool-down, below about 70 °C, and should be combined with glycols or organic acids for broad-spectrum coverage.

For synergy:

Use a biodegradable chelator such as sodium phytate, GLDA or MGDA in almost all modern formulas, especially those rich in botanicals and clays.
Build a glycol stack with humectants like glycerin and pentylene glycol to reduce water activity and support weak-acid systems.
Choose airless or controlled-orifice packaging where possible to reduce back contamination, particularly for facial care and high-botanical systems.

These small design choices make natural preservatives behave more like a well-tuned system and less like a fragile add-on.

Claims, Compliance And Staying Honest

A quick reminder before leaving you: a good preservative system does not give you a free pass on proper stability & preservative efficacy testing. Additionally, whatever natural preservative system you choose, your marketing claims still need to respect EU common criteria for cosmetic claims: lawful, truthful, supported, fair, honest and allowing consumers to make informed decisions.

Avoid implying that conventional preservation is “unsafe” or “toxic” when your own products rely on benzyl alcohol, organic acids, glycols or ferments that are also preservatives under EU law. Keep your INCI lists accurate, declare fragrance allergens where thresholds are met, and document your preservation strategy, challenge test results and pH control in your Product Information File so that it will travel smoothly between the EU, UK and other regions.

Some natural preservative systems fail because their acids are weak, others fail when pH, solubility, chelation, water activity and packaging are treated as afterthoughts. So do your own research and thoroughly test your chosen options before settling on a preservative system.

Here’s to formulas that work and brands that thrive!

From my lab to yours,

Rose