What is DPG (dipropylene glycol), and how do you use it in perfume?
By Omer Siton, founder of PerfuMate · Updated
Dipropylene glycol, DPG, is a practically odorless, colorless solvent that perfumers use to dilute strong or solid materials, to make 10% dilutions for weighing, and to carry oil-based and functional fragrances. It barely evaporates and adds weight to a formula but no smell, which is the one thing to remember every time you weigh it.
What is dipropylene glycol, and why do perfumers use it?
DPG is a glycol solvent: a mixture of three closely related isomers sold under one CAS number, 25265-71-8, made as a co-product of propylene glycol. Dow describes its fragrance grade as practically odorless, colorless, water-soluble and hygroscopic, and PerfuMate's catalog calls Dipropylene glycol the perfumer's workhorse diluent, adding that a fragrance, low-odor, grade is essential.
Perfumers use it to make dilutions of strong materials, to dissolve crystals such as Ambroxan and Vanillin, and as the carrier of some oil-based and functional fragrances. Is it natural? No: the catalog files it as synthetic, an industrial co-product. Does it contain alcohol? It contains no ethanol: DPG is a glycol, chemically a different kind of alcohol from the ethanol in perfume. Does it evaporate? Very slowly. It boils at about 231 °C, against 78 °C for ethanol, and its vapor pressure at room temperature is more than a thousand times lower, so it stays on the skin or the strip with the perfume.
How much DPG should go in a perfume?
As little as your dilutions need: an alcohol perfume needs no DPG at all, and every gram of it adds weight without smell, so it lowers the real concentration. There is no standard percentage. In ready-made fragrance oils the share can be large; Dow's data sheet for its fragrance grade notes that in perfumes DPG sometimes makes up more than half of the formulation, so ask a supplier how much of an oil is solvent.
A worked example. The 10 g first formula on how to make perfume at home weighs Ambroxan and Vanillin as 10% solutions in DPG, 1 g and 0.5 g. Those two lines bring 1.35 g of DPG, so the concentrate is 8.65 g of aromatic material and 1.35 g of solvent. Weigh 4.5 g of it into a 25 g bottle and the perfume is 15.6% aromatic, not 18%. For a true 18%, weigh 5.2 g of concentrate and 19.8 g of alcohol. Perfume oil to alcohol ratio explains why the concentration has only one definition.
PerfuMate counts it the same way: since version 1.3.53, a solvent line adds weight to the formula but no strength to the concentration shown, and the IFRA calculator reads a line written "Ambroxan 10% in DPG" as one tenth Ambroxan.
Perfumer's alcohol vs DPG: which solvent, and when?
Use perfumer's alcohol to dilute the finished perfume, and DPG or another non-evaporating solvent to dilute single materials and to carry formats that should not evaporate; they are not interchangeable, and DPG is not the same thing as perfumer's alcohol. Alcohol flashes off within minutes, lifting the top notes and leaving the perfume behind; DPG stays on the skin with the perfume and, as the catalog puts it, slows evaporation slightly. A spray made in DPG instead of alcohol does not dry like a perfume.
| Job | Perfumer's alcohol | DPG |
|---|---|---|
| Diluting a finished eau de parfum or eau de toilette | Yes, this is its job | No |
| 10% dilutions for weighing | Yes: the solvent becomes part of the perfume's alcohol, but a loose cap lets it evaporate and the dilution grows stronger than its label | Yes: stable in the bottle, but the solvent stays in the perfume and lowers its strength |
| Dissolving crystals such as Ambroxan or Vanillin | Yes | Yes |
| Perfume oils and solid perfumes | No, they are made without alcohol | As a small helper to dissolve crystals before the carrier goes in |
The perfumer's alcohol itself is covered on what alcohol to use for perfume.
DPG vs propylene glycol: what is the difference?
They are related glycols but not the same material: propylene glycol (PG, 1,2-propanediol, CAS 57-55-6) is a single, smaller molecule, and DPG a mixture of larger isomers made alongside it. PG boils at about 188 °C and DPG at about 231 °C, and the catalog notes that Propylene glycol is less universal for aroma chemicals than DPG, with limited solvency for very nonpolar materials, though ideal where water miscibility is needed. For perfume dilutions, DPG is the usual choice.
Is DPG safe?
As used in cosmetics and perfume, the assessments say yes. The US Cosmetic Ingredient Review panel concluded in 1985 that dipropylene glycol is safe as presently used in cosmetics, and in the notifications companies have filed with the EU's classification and labelling inventory, almost all report that it does not meet the criteria for any hazard class.
It is not flammable in the everyday sense. Its flash point is about 120 to 138 °C depending on the test, with Dow giving 124 °C closed cup, against about 13 °C for ethanol, so a perfume's flammability comes from its alcohol, not its DPG. Handle it like any solvent: keep it out of your eyes, and keep the bottle closed, because it draws water from the air.
Where can I buy DPG?
From perfumery suppliers and chemical distributors. Ask for a fragrance, low-odor, grade, which the catalog calls essential, and for the supplier's safety data sheet. Where to buy perfume materials covers how to choose a supplier.
In PerfuMate, DPG is a catalog material marked as a solvent: a dilution made from stock becomes its own bottle with its strength and solvent, every line is corrected for the bottle it is weighed from, and the concentration counts solvent as weight, not strength. The free dilution calculator works out how much solvent a dilution needs.
Sources: Dow, Dipropylene Glycol LO+ technical data sheet and propylene glycols; PubChem, dipropylene glycol (boiling point, vapor pressure, flash point, ECHA notifications summary), propylene glycol and ethanol; NIOSH Pocket Guide, ethyl alcohol (flash point); Cosmetic Ingredient Review, Final report on the safety assessment of butylene glycol, hexylene glycol, ethoxydiglycol and dipropylene glycol, Journal of the American College of Toxicology 4(5), 1985 (EPA HERO record).