Humectants: Dipropylene glycol & butylene glycol

Dipropylene glycol shares many of the characteristics of propylene glycol, but it has a higher boiling point (232.2˚C vs. 188˚C for propylene glycol) and a higher molecular weight. It's used more as a fragrance fixative than a humectant, although it can behave as a hygroscopic ingredient. It will reduce the freezing point of your products and make your surfactant mixes clearer. It is soluble in water, alcohol, and castor oil. It is a viscous, colourless, slightly sweet tasting (with a bitter aftertaste) liquid.

Dipropylene glycol is used a lot in fragrance oils, and you might see suppliers listing their fragrances as DPG free. It's a great fragrance fixative, although fragrances with DPG can cloud and soften translucent soap bars, so if you're a melt & pour type girl like me, watch out when you're using a clear soap! (It's actually used in shaving bars to make them softer because that's a bonus for that product!) You will notice a difference in non-DPG fragrances - they tend to fade quicker than those with it - so you can extend the life of the scent by adding some DPG or C12-15 alkyl benzoate to your product.

You can use it at up to 50% in the heated water phase of your product, although you'll probably want to use it at 1% to 5% or so. It's a good option for deodorant bars as a gelling agent, and you can use it at up to 10% in that capacity.

Butylene glycol (1,3-butanediol or 2,3-butanediol) is related to the other glycols in that it is also a polyol or polyalcohol (as indicated by those little OHs on the carbon chain). It is soluble in water, acetone, and castor oil. Like the other glycols, it is a viscous, colourless, slightly sweet tasting (with a bitter aftertaste) liquid. It is also a humectant, but it is the most resistant to high humidity than the other glycols, which means it's great for very humid areas. Butylene glycol can be used to retard the loss of fragrances in our products - so if you have a body spray that keeps losing its scent, a little butylene glycol can help retain that lovely fragrance. It's skin irritation is very low - the lowest amongst the glycols - and it is considered safe by pretty much every agency.

You can use butylene glycol at up to 89% in the heated water phase of your product, but you'll probably want to keep it around 1% to 5%. You can use this as the gelling agent in deodorant bars, and you can use it at up to 10% in that capacity.

Join me tomorrow to take a look at mineral oil (insert dramatic chord here!).