Butylene Glycol
A lightweight humectant and solvent — like propylene glycol, but lower-irritation and lower-allergy (often the "PG-free" swap)
INCIButylene Glycol
- Category
- Humectant
- Risk level
- low
- What it is
- A small four-carbon glycol — humectant + solvent + slip/viscosity agent
- vs propylene glycol
- Less sticky and lower-irritation; common as a "PG-free" replacement
- Tolerability
- Very low allergy; cross-reactivity with propylene glycol is low
- Where it shines
- Lightweight toners, essences, and gels (often top-3 in K-beauty formulas)
Look for these names on ingredient lists
This ingredient may appear under any of these names:
Commonly found in
Possible reactions
- Contact dermatitis very rare (well under 0.1%)
- No comedogenic effect at cosmetic concentrations
- Brief stinging only at very high concentrations on broken skin
- Generally tolerated by those sensitive to propylene glycol
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Always scan the actual label before use — formulations change.
What is butylene glycol?
Butylene glycol is a small four-carbon glycol — a colourless, syrupy liquid that multitasks in cosmetic formulas. It's a humectant (pulls water into skin), a solvent (dissolves botanical extracts and actives so they spread evenly), and a slip/viscosity agent (gives toners and lotions their texture).
Chemically it's a cousin of propylene glycol with one extra carbon — and that small difference makes it less sticky and lower-irritation, which is why modern Korean and Japanese skincare leans on it heavily.
Why it's almost never a problem
Safety panels have reviewed butylene glycol repeatedly and rate it safe at the levels used (usually 1–10%). Patch-test contact dermatitis runs well under 0.1% — rarer than propylene glycol or even fragrance. A few notes, none alarming:
- PG cross-reactivity is low. If you've reacted to propylene glycol, butylene glycol is usually a safe try.
- High concentrations (over ~30%) can briefly sting broken skin — mechanical, not allergic.
- "Glycol-free" purism has no scientific basis here — butylene glycol isn't toxic, endocrine-disrupting, or bioaccumulative.
How to use it well
- Don't avoid it for the name — it's one of cosmetic chemistry's gentlest ingredients.
- Expect it in lightweight formulas — toners, essences, gels, sunscreens.
- It's a layering helper — as a solvent it carries other actives in, so a good butylene-glycol toner makes what follows work better.
- Seal in dry climates with a cream/oil on top.
- Try it if PG bothers you.
Alternatives
- Reacted to butylene glycol itself? glycerin, pentylene glycol, sodium PCA.
- Very sensitive skin: sodium PCA, panthenol, hyaluronic acid (near-zero reactions).
- Very dry skin: heavier humectants (glycerin, urea) hold water longer.
The bottom line
Butylene glycol is a featherweight, low-allergy humectant-and-solvent that makes light formulas feel good and helps actives absorb. Ignore the "glycol = bad" myth; if propylene glycol irritates you, this is usually the easy, well-tolerated swap.
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