Dipropylene Glycol

Overview

Dipropylene glycol (DPG) is a clear, colourless, nearly odourless liquid that serves as the invisible backbone of the fragrance and home-fragrance industries. It’s the solvent that dilutes pure fragrance oils to workable concentrations, the carrier in reed diffusers that wicks up the sticks, and the base of many body sprays and room mists.

Chemically, it’s a dimer of propylene glycol — two propylene glycol units linked together. This makes it less volatile, less hygroscopic, and a better solvent for aromatic compounds than propylene glycol itself. Its near-zero odour is crucial: it dissolves fragrance oils without contributing any scent of its own, letting the perfume speak for itself.

Beyond perfumery, DPG shows up in skincare as a lightweight humectant (it attracts and holds moisture, though less powerfully than glycerin) and as a solvent for difficult-to-dissolve actives. It has good skin compatibility, low toxicity, and evaporates slowly — properties that make it versatile across product categories.

What it does in a formula

DPG fills several roles depending on context:

1. Fragrance diluent — the primary use. Perfumers dilute concentrated aroma chemicals and essential oils in DPG to create 10-20% solutions for blending, testing, and formulating. It’s the standard “base” for fragrance oils sold to the craft market.
2. Reed diffuser base — DPG’s low viscosity, low volatility, and excellent capillary action make it ideal for wicking up rattan reeds and releasing fragrance slowly.
3. Room and body spray solvent — dissolves fragrance at high concentrations without the strong evaporative cooling of alcohol. Good for alcohol-free spray formulations.
4. Humectant — milder than glycerin, less sticky, no tacky feel. At 3-10% in skincare, it provides light hydration and helps dissolve water-shy actives.
5. Coupling solvent — helps oil-soluble and water-soluble ingredients coexist in a single phase, reducing the need for surfactant-based solubilizers.

How to use

• Fragrance dilution: Dissolve fragrance oils or EOs at 10-30% in DPG for safe handling and accurate measuring. Stir until clear. No heat needed.
• Reed diffusers: 60-80% DPG + 20-40% fragrance oil. Insert rattan reeds. Flip reeds every few days to refresh scent throw.
• Room sprays (alcohol-free): 70-80% DPG + 10-20% fragrance oil + 5-10% water (optional). Shake and spray.
• Body sprays: 40-60% DPG + 5-15% fragrance oil + water to 100%. May need a solubilizer if water content is high and clarity matters.
• In skincare (humectant/solvent): 3-10%. Add to water phase or any phase — DPG is compatible with both oil and water systems.
• Temperature: Room temperature for all applications. No heating needed.
• Compatibility: Stable across all practical pH ranges. Non-reactive with most cosmetic ingredients.

Best for / Worst for

Best for: perfume dilution, reed diffusers, alcohol-free room sprays, body mists, fragrance oil blending, dissolving difficult actives, light humectant in skincare, coupling solvent in tricky formulas.

Worst for: anhydrous balms and butters (no reason to add it — use an oil), products marketed as “glycol-free,” formulas where you need strong humectancy (glycerin or hyaluronic acid are better), products meant to evaporate quickly (DPG evaporates slowly — use alcohol for fast-dry sprays).

Common pitfalls

Expecting strong humectant performance. DPG is a mild humectant compared to glycerin, propanediol, or hyaluronic acid. If hydration is your goal, DPG alone won’t deliver — it’s better thought of as a solvent that happens to have humectant properties.

Using as a perfume solvent when alcohol is expected. Traditional fine fragrance uses ethanol because it evaporates and projects scent into the air. DPG doesn’t evaporate readily — it stays on skin or fabric, providing longer-lasting but lower-sillage scent. Different tools for different goals.

Overuse in leave-on skincare. Above 10-15% in a leave-on product, DPG can feel slightly slippery or “filmy” on skin. Fine in a mist, less desirable in a serum.

Confusing DPG with propylene glycol. They’re related but different. Propylene glycol is smaller, more hygroscopic, and a better humectant. DPG is larger, less hygroscopic, and a better fragrance solvent. Not interchangeable in perfumery.

Reed diffusers not wicking. If your diffuser isn’t throwing scent, the issue is usually reed quality (must be rattan with open channels), not DPG. Flip more frequently or use more/thicker reeds.

Substitutes

• Ethanol (perfumer’s alcohol) — fast-evaporating, high sillage, traditional fine-fragrance solvent.
• Propylene glycol — similar but smaller molecule, stickier, better humectant, worse fragrance solvent.
• Isopropyl myristate — oil-soluble carrier for fragrances in oil-based perfumes.
• Triethyl citrate — natural alternative fragrance solvent, mild citrus note.
• Diethyl phthalate (DEP) — traditional fixative/solvent (being phased out due to safety concerns — avoid).