Modern cosmetic formulas increasingly move away from traditional parabens and formaldehyde donors toward "multifunctional" ingredients that boost a small dose of mainstream preservative — or, in carefully designed systems, replace it entirely. Two workhorses dominate this space: phenoxyethanol (CAS 122-99-6) and 1,2-hexanediol (CAS 6920-22-5). They are often discussed as alternatives, but in practice they play different roles and are frequently used together.
What each ingredient does
Phenoxyethanol is a glycol ether with broad antimicrobial activity, particularly against gram-negative bacteria. It is a globally accepted, well-documented preservative used at up to 1.0% in the EU and US. Its weakness is limited efficacy against fungi and mold at practical use levels, which is why it is almost always paired with a second booster.
1,2-hexanediol is a linear diol that works primarily by reducing water activity in the formula, making the environment hostile to microbes. On its own it is a modest antimicrobial; at 2–5% it is an excellent partner for organic acids (dehydroacetic acid, benzoic acid, sorbic acid, levulinic acid) and for phenoxyethanol, and it contributes a light, non-tacky emollient feel.
Side-by-side comparison
| Phenoxyethanol | 1,2-Hexanediol | |
|---|---|---|
| CAS No. | 122-99-6 | 6920-22-5 |
| Typical use level | 0.5–1.0% | 2–5% |
| Regulatory limit | 1.0% max (EU Annex V #29, also US/China/Japan) | None specific (not a listed preservative in EU Annex V) |
| Main strength | Broad antibacterial action, global acceptance | Water-activity reduction, fungistatic support, skin feel |
| Main weakness | Weak against fungi alone; 1% cap limits flexibility | Low antimicrobial potency alone; needs higher dose |
| Skin feel | Slightly oily, can feel warm at high dose | Dry, light emollience at 2–5% |
When to choose which
- Simple O/W emulsions for global markets — phenoxyethanol 0.8% + 1,2-hexanediol 2% is a proven, low-irritation baseline that passes PCCT (double challenge testing) in most formula types.
- "Preservative-free" or natural-positioned formulas — 1,2-hexanediol combined with glyceryl caprylate and an organic acid (e.g. sodium levulinate / sodium anisate) is the classic booster system; verify with a full preservative challenge test (ISO 11930).
- High-water gels and toners — 1,2-hexanediol at 3–5% doubles as a humectant-light emollient and dissolves readily in the water phase.
- Formulas sold in the EU — remember phenoxyethanol counts toward the 1.0% Annex V limit regardless of claims on the front of the pack.
Practical formulation notes
Both ingredients are water-soluble and heat-stable, so they can be added to the water phase at any stage — but adding them below 40°C at the end of the process minimizes any volatile loss of phenoxyethanol. 1,2-hexanediol is also an effective solubilizer for some preservative actives and fragrance materials. If your formula contains high levels of electrolytes or nonionic surfactants, run a dedicated compatibility check — booster systems are sensitive to formula architecture, and a passing PET result in one formula never transfers to another.
We supply 1,2-hexanediol (CAS 6920-22-5) and glyceryl caprylate with full TDS/COA/MSDS documentation. Tell us your formula type and target market, and our team will recommend a compliant preservation strategy with current pricing.