In the fast evolving world of beauty and skincare, innovation often pushes formulations into new territory. Nanoemulsions, microemulsions and advanced delivery systems are now central to product strategies for brands that want superior sensory profiles, enhanced penetration and elevated performance. Yet as formulations become more sophisticated, so do the challenges behind the scenes. One of the most underestimated challenges is the preservation of systems that contain a high concentration of nonionic surfactants.

A recent scientific study offers valuable insight into how preservatives behave in these modern systems and why many traditional approaches fail. For formulators, regulatory teams and brand leaders, understanding these interactions is essential for product safety, stability and commercial success.

At Olalla Consulting, we support brands and manufacturers in navigating exactly these complexities. This article breaks down the key findings of the research and translates them into practical guidance for real world product development.

Why High Surfactant Systems Challenge Preservation

Nanoemulsions and microemulsions rely on significant levels of polyethoxylated surfactants such as polysorbate 80 and hydrogenated castor oil. These ingredients create elegant textures and stable structures, but they also interact with preservatives in ways that reduce antimicrobial activity.

The study found that:

• Nonionic surfactants can bind or solubilise preservatives
• This reduces the free preservative available in the aqueous phase
• As a result, antimicrobial performance drops significantly

This is especially true for parabens, which are widely used in cosmetic preservation but are known to be sensitive to interactions with highly ethoxylated materials.

For brands working with advanced emulsions, this means that a preservative system that performs perfectly in a standard cream may fail entirely in a nanoemulsion.

How Parabens Behave in High Surfactant Systems

The research confirmed what many formulators have observed in practice. Parabens such as methylparaben and blends containing methyl, ethyl, propyl, butyl and isobutyl parabens lose their effectiveness when combined with high levels of polysorbate 80 or hydrogenated castor oil.

In the study:

• Methylparaben at 0.2 percent was not able to reduce microbial growth by the required two log reduction
• The paraben blend PMEPBI also showed poor performance
• In some cases, microbial counts increased between day 14 and day 28

This is a clear indication that parabens become unavailable due to micellar solubilisation or binding to surfactant structures.

For brands still relying on paraben systems, this is a critical reminder that compatibility testing is not optional. It is essential.

Paraben Free Systems Show Greater Stability

The study also evaluated two paraben free systems:

• Phenoxyethanol with sodium benzoate
• Phenoxyethanol with caprylyl glycol

These systems performed better overall, although not universally. Phenoxyethanol based blends were less affected by surfactant interactions, but still showed reduced performance in certain conditions.

Key findings include:

• Phenoxyethanol and sodium benzoate (BP) showed the strongest overall performance
• Phenoxyethanol and caprylyl glycol (PC) was effective against some organisms but not all
• Even the best performing systems struggled in microemulsions and nanoemulsions when surfactant levels were very high

This reinforces the need for tailored preservation strategies rather than relying on standard usage levels.

Why Challenge Testing Must Reflect Real Formulations

One of the most important insights from the study is that preservative performance in isolation does not predict performance in a finished formulation.

A preservative may pass compatibility testing with individual excipients but still fail once incorporated into a complex emulsion. This is because:

• Surfactant levels change the availability of the preservative
• Oil phase composition influences partitioning
• Processing conditions affect distribution
• The final structure of the emulsion determines how much preservative is free to act

This is why at Olalla Consulting we always recommend challenge testing on the final formulation, not on a theoretical model or simplified base.

If you want support with challenge test planning or preservative strategy, you can explore our Regulatory and Compliance Services on the Olalla Consulting website.

What This Means for Beauty and Skincare Brands

For brands developing modern emulsions, the implications are clear:

1. Parabens are not suitable for high surfactant systems

Their antimicrobial activity is significantly reduced, making them unreliable for nanoemulsions and microemulsions.

2. Paraben free systems perform better but still require careful optimisation

Phenoxyethanol based blends are more robust but not universally effective.

3. Preservative blends may be necessary

Single molecule systems rarely provide broad spectrum protection in advanced emulsions.

4. Every formulation must undergo a tailored preservation strategy

There is no one size fits all solution. Preservation must be designed around the specific surfactant system, oil phase and processing method.

5. Challenge testing is essential for regulatory compliance and product safety

This is not just a regulatory requirement. It is a brand protection strategy.

If you want to learn more about formulation optimisation, you can visit our Formulation Development page at Olalla Consulting.

How Olalla Consulting Supports Your Preservation Strategy

With decades of experience across formulation science, regulatory compliance and brand development, Olalla Consulting helps companies create safe, stable and commercially successful products.

We support you with:

• Preservative system selection
• Compatibility assessments
• Challenge test planning and interpretation
• Nanoemulsion and microemulsion formulation
• Regulatory documentation for global markets
• Supplier evaluation and ingredient strategy

If you are developing a high surfactant formulation or planning to introduce nanoemulsion technology into your product line, our team can help you design a preservation system that is both effective and compliant.

Ready to Strengthen Your Preservation Strategy?

If you want expert guidance on preservative selection, formulation optimisation or regulatory compliance, Olalla Consulting is here to support you.

Visit our website to explore our services or contact us directly to discuss your project.

Your next breakthrough deserves the right scientific foundation. Let us help you build it.