Short answer: pentylene glycol (1,2-pentanediol) is the more water-soluble, more humectant, higher-loading option and is particularly associated with anti-acne and toner formats. 1,2-hexanediol is more lipophilic, dries lighter, and is the more common booster in emulsion preservation systems. Neither is a stand-alone preservative.
Side-by-side comparison
| Property | 1,2-Pentanediol | 1,2-Hexanediol |
|---|---|---|
| INCI name | Pentylene Glycol | 1,2-Hexanediol |
| CAS number | 5343-92-0 | 6920-22-5 |
| EC number | 226-285-3 | 230-029-6 |
| Molecular formula / weight | C5H12O2 / 104.15 g/mol | C6H14O2 / 118.17 g/mol |
| Density (25 °C) | ≈ 0.971 g/cm³ | ≈ 0.951 g/cm³ |
| Boiling point | 206 °C | 223–224 °C |
| Water solubility | Miscible | Good, but markedly lower; high loadings can cloud water-thin systems |
| Oil solubility | Low | Higher |
| Humectancy | Higher; adds slip to the water phase | Moderate; dries lighter |
| Antimicrobial role | Broad antibacterial activity, including against C. acnes | Antibacterial booster, very widely paired with phenoxyethanol |
| Typical use level | 0.5–5 % | 0.5–3 % |
| Regulatory status (EU) | Multifunctional ingredient; not listed in Annex V | Multifunctional ingredient; not listed in Annex V |
| Strongest fit | Toners, essences, anti-acne, baby care, wet wipes | Emulsions, masks, preservative-reduced concepts |
What one extra carbon actually changes
Both molecules are 1,2-diols: two adjacent hydroxyl groups on a short alkyl chain. The chain length controls how the molecule partitions between water and oil. With five carbons, pentylene glycol is miscible with water and only weakly surface-active. With six, 1,2-hexanediol becomes noticeably more lipophilic: it still dissolves in water, but at higher concentrations in low-viscosity aqueous systems it can haze or form a separate phase, and it partitions into the oil phase and into cell membranes more readily.
That partitioning is also why the two behave differently in preservation. Greater membrane affinity generally means more antimicrobial activity per percent — which is why hexanediol is typically used at 0.5–3 % while pentylene glycol is often used at 2–5 % to get a comparable effect.
Preservation: what these ingredients are and are not
Neither substance is listed in Annex V of Regulation (EC) No 1223/2009, so neither can be declared as a preservative on an EU label. They are marketed as multifunctional ingredients — humectant, solvent, skin-conditioning agent — whose antimicrobial activity allows formulators to reduce the level of a listed preservative or to work with a “preservative-light” positioning.
In practice both are used as boosters. Pentylene glycol pairs well with phenoxyethanol and ethylhexylglycerin in toners and essences, and has a long history in anti-acne products because of its activity against Cutibacterium acnes. 1,2-Hexanediol is the more common choice in emulsions, where its slight lipophilicity helps it reach the oil–water interface where microbes concentrate.
Whatever you claim, the evidence has to come from a challenge test to ISO 11930 or an equivalent method on the finished formula. A “preservative-free” claim based on the ingredient list alone will not survive a regulatory review or a retailer's technical audit.
Skin feel and where the difference is felt
Pentylene glycol is a slightly better humectant and adds noticeable slip at 3–5 %; at the top of its use range it can feel faintly tacky on its own, which is why it is usually combined with lighter glycols in serums. 1,2-Hexanediol dries down cleaner and leaves less residue, which suits emulsions and masks where the glycol is present for preservation rather than for its own sensory contribution.
In a water-thin product — a toner or a micellar water — the solubility difference is the practical constraint rather than the feel. If you want 4–5 % of a glycol in a low-surfactant aqueous system, pentylene glycol will stay clear where hexanediol may not.
Choosing between them
Water-thin system with a high glycol load?
Pentylene glycol. Miscibility removes the cloud point question entirely.
Emulsion or mask, boosting a phenoxyethanol system?
1,2-Hexanediol. The lipophilic character and the 0.5–3 % use level fit the format, and it is the better-documented pairing.
Anti-acne or oily-skin positioning?
Pentylene glycol, for its documented activity against C. acnes and its lighter humectant profile at higher loading.
Sensory target is “nothing on the skin”?
1,2-Hexanediol at the lower end of its range.
Cost per tonne of finished product?
Calculate at equal antimicrobial performance, not at equal weight. Hexanediol's higher price per kilogram is offset by its lower use level, and at 0.5–3 % the difference in a finished tonne is usually small.
Using them together
The two are frequently blended. A typical system might use 2 % pentylene glycol for humectancy and antibacterial support plus 1 % 1,2-hexanediol for interfacial activity, alongside 0.5–1 % phenoxyethanol. Blending widens the spectrum and reduces the chance that a single organism survives the challenge test, which matters most in products with a high water activity and a pH near neutral.
Specification and supply
We supply both at ≥ 99.5 % (GC), cosmetic grade, in 25 kg net HDPE drums or 200 kg net iron drums, with 1 kg evaluation packs. Both are colourless clear liquids and both carry a Category 2 eye-irritation classification (H319) under GHS, so eye protection is the normal handling precaution in the laboratory. English SDS and batch-specific CoA are available for either product.