Butylene Glycol

Overview

Butylene glycol (sometimes called 1,3-butylene glycol or 1,3-butanediol) is a clear, colourless, slightly sweet-smelling small molecule. It is a humectant, a solvent for botanical extracts, and a co-solvent in clear gel formulations. You will find it in serums, ampoules, toners, and any “watery” product where the finished texture needs to be smooth, clear, and non-sticky.

The reason formulators reach for it over glycerin: butylene glycol is much less tacky. At 5-10% in a serum, glycerin can feel sticky on the skin; butylene glycol at the same percentage feels almost weightless. The reason formulators reach for it over propylene glycol: it has a cleaner safety profile and is less drying.

There are bio-derived (corn-fermented) and synthetic versions. The bio-derived one carries a higher price but is COSMOS-eligible.

Shelf life is 2-3 years. It is microbially stable and chemically inert.

What it does in a formula

Three roles, often simultaneously:

1. Humectant — draws moisture from the air into the upper layer of the skin (less efficiently than glycerin per gram, but still meaningful at 3-10%).
2. Solvent — dissolves botanical extracts, glycerites, and some preservatives that struggle in pure water. Many extracts are sold pre-dissolved in butylene glycol for this reason.
3. Slip and feel modifier — gives a clean, satisfying glide in toners and gels without the heaviness of glycerin.

Useful side bonus: it has mild antimicrobial activity at 5% and above, which slightly reduces the load on your main preservative.

How to use

Add to the water phase, or to a cool-down cold water phase if your preservative is unstable to heat. Butylene glycol is stable up to 90 C, so heating with the rest of the water phase is fine.

Usage rates by product type:

• Hydrating toners: 3-10%
• Watery serums and ampoules: 5-15%
• Light gel-cream lotions: 3-8%
• Sheet mask essences: 5-15%
• Sprays and mists: 1-5%
• Solvent for botanical extracts: 3-10% (or whatever the extract is dissolved in)
• Anhydrous oil products: not applicable (it is water-soluble)

For a clear hydrating serum, 5-10% butylene glycol + 2% glycerin + 1% sodium hyaluronate gives you the right balance of humectant action and dry-touch finish.

Best for / Worst for

Best for: Korean-style ampoules and essences, clear gels, hydrating toners, mist sprays, watery hyaluronic serums, oil-control hydrating products, summer-formula moisturisers, products where you want a no-stick finish.

Worst for: very dry mature skin (it is a less effective humectant than glycerin, and you lose the cushioning), strict “minimalist” formulations where you want one humectant doing all jobs, very water-rich products that need viscosity (butylene glycol thins formulas slightly).

Common pitfalls

Confusing it with propylene glycol. They are related but not identical. Propylene glycol is more controversial for irritation; butylene glycol is the gentler cousin. Substituting one for the other 1:1 usually works but pay attention to skin tolerance.

Overusing it. Above 20-25% in a watery formula, you start getting a slight cooling-then-tight feel that signals over-humectant load. Stay in the 3-15% range for most products.

Choosing the cheaper synthetic version when you market natural. Bio-derived butylene glycol from corn fermentation is COSMOS-approved; the synthetic version is not. If you sell to that market, double-check your supplier’s certification.

Treating it as a preservative. Mild antimicrobial support, yes. Full preservative, no. You still need a proper preservative system.

Substitutes

• Pentylene glycol — closely related, slightly longer chain, also a mild preservative booster, slightly more substantive feel.
• Propanediol (1,3-propanediol, plant-derived) — corn-fermented humectant with almost identical feel and function. Many formulators are switching to this for natural credentials.
• Glycerin — much cheaper, more humectant power per gram, much more tacky feel.
• Sodium PCA — natural-feeling humectant with a different mechanism.
• Propylene glycol — older, cheaper, slightly higher irritation potential.