- Sep 3
- 3 min read
Optiphen Plus is a widely used preservative system in cosmetic formulation, especially popular among DIYers and small-scale formulators. While it is not COSMOS-approved, it is still globally accepted because it is paraben-free and formaldehyde-free, making it an appealing option for those looking for a broad-spectrum preservative.
The key reason it is not COSMOS-approved comes down to phenoxyethanol, which makes up about 52% of the blend. Still, Optiphen Plus remains one of the most accessible and effective preservation systems for emulsions—when used correctly.
Unfortunately, I’ve seen countless online posts where formulators run into issues with emulsion separation or viscosity changes after adding Optiphen Plus. So, why does this happen, and how can you avoid it? Let’s break it down.
What is Optiphen Plus?
Manufacturer: Ashland
INCI: Phenoxyethanol (and) Caprylyl Glycol (and) Sorbic Acid
Usage Rate: 0.75% – 1.5%
Solubility: Limited in water; soluble in glycols (propylene glycol, butylene glycol), glycerin, ethanol, and isopropanol.
Best Use: Emulsions (lotions, creams, serums).
Not Ideal For: High-water products like toners, facial mists, or micellar waters.
Why Do Formulators Struggle With Optiphen Plus?
Despite being effective, Optiphen Plus is pH-sensitive and requires careful handling. Here are the most common reasons it “fails”:
1. Narrow pH Range
Optiphen Plus is only effective in the range of pH 4.0–6.0, with an ideal sweet spot between 4.8–5.5. Many DIYers don’t realize how critical this range is, leading to ineffective preservation or destabilized emulsions.
Tip: Always test your formulation’s pH with a quality pH meter. Never rely on strips—they only provide whole-number readings, making them useless for fine-tuning.
2. pH Drift Over Time
Every cosmetic product experiences pH drift during its shelf life (often ~10%). The challenge is that the drift can go up (more alkaline) or down (more acidic), and there’s no way to predict which way it will go.
This means formulators must design products with pH buffering in mind to ensure Optiphen Plus remains within its effective range for the entire 2–3 year shelf life expected of most cosmetics.
3. Blaming the Wrong Ingredient
Sometimes the issue isn’t Optiphen Plus at all. A formulation may be unstable due to emulsifier choice, oil phase percentage, or mixing method. Optiphen Plus is often unfairly blamed because it is added last, and separation happens afterward.
My Experience With pH Meters
I’ve tested several inexpensive pH meters in the $30–$80 range, but most were inaccurate or stopped working within months. Eventually, I invested in a Hanna pH meter—it’s not cheap, but the accuracy and longevity make it worthwhile.
Here are a few non-affiliate links for reliable meters if you’re serious about formulation:
Optiphen Plus is not an unreliable preservative—it’s simply misunderstood. When used within its proper pH range and in the right type of formulation (emulsions, not toners), it can provide reliable broad-spectrum protection.
To use Optiphen Plus properly, remember:
✔ Keep your formulation pH between 4.8–5.5
✔ Account for pH drift over time
✔ Use a quality pH meter (not strips)
✔ Avoid high-water products where it won’t perform well
By respecting these guidelines, you’ll find that Optiphen Plus is not only effective but also a practical choice for many natural-inspired formulations.
If you are not familiar with adjusting pH, check out this blog post:
