It meets four demanding requirements at once. It is essentially odourless, so it does not distort the composition; it dissolves both the oil-soluble and the polar components of a fragrance concentrate; it is low in toxicity and non-sensitising, which matters because it ends up on skin at high proportion; and its volatility is low enough not to alter the evaporation profile of the perfume.
2
Why is perfumery grade specified separately?
Because odour depends on purity. Trace impurities that would be irrelevant in an industrial application are immediately detectable in a fragrance and will alter the composition. Perfumery grade DPG is specified on odour as a formal parameter alongside assay and water content, and industrial grade is not an acceptable substitute.
3
Is DPG a single compound?
No, it is supplied as a mixture of isomers, which is normal for dipropylene glycol. The joining of two propylene glycol units can produce several structural arrangements, and commercial material contains a characteristic distribution. This does not affect its performance as a diluent, since all the isomers share the relevant properties.
4
Is DPG safer than DEG?
Yes, substantially. DPG is a propylene-series glycol metabolised by routes that do not produce the nephrotoxic acids that make DEG dangerous, and it has low acute toxicity. That is one reason it is used in cosmetics and fragrance at high inclusion while DEG is restricted to industrial applications.
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