What Is Propylene Glycol?
Propylene glycol (INCI name: Propylene Glycol, occasionally listed as 1,2-propanediol) is a clear, odourless, water-miscible liquid alcohol. It is synthetic, and it has been used in cosmetics, medicines and food for decades.
In a skincare formula it wears several hats at once. According to the Cosmetic Ingredient Review, the industry's independent safety panel, propylene glycol functions as a skin-conditioning agent, solvent, viscosity-decreasing agent and fragrance ingredient. In practice that means it:
- Dissolves active ingredients that wouldn't otherwise mix into a water-based formula
- Carries water into the upper layers of skin as a humectant
- Improves the texture and spreadability of a product
- Helps formulas stay stable through temperature changes
It is typically used at concentrations between roughly 1% and 10% in leave-on skincare, though it can go higher in some formulations.
The Benefits for Skin
It's a humectant. Propylene glycol has a high affinity for water. It draws moisture towards the skin's surface and helps hold it there, which leaves skin looking plumper, softer and less flaky. This is why it appears so often in hydrating serums and moisturisers — it's an efficient, inexpensive way to boost a formula's moisturising power.
It helps other ingredients get where they're going. This is the benefit that gets least credit. Propylene glycol is a well-documented penetration enhancer. Research shows it works by partitioning into the stratum corneum — the skin's outermost barrier — where it interacts with the lipid bilayer, temporarily increasing permeability so active ingredients can cross the barrier more effectively. A 2024 study in the International Journal of Molecular Sciences found that propylene glycol localises at the bilayer interface and occupies lipid–water hydrogen-bonding sites, which is how it opens the door for other molecules.
In plain terms: the vitamin C, retinol or niacinamide in your serum is more likely to do its job when propylene glycol is in the formula alongside it. It is often used in combination with other enhancers, and the effect tends to be synergistic.
It makes formulas feel better. As a solvent and viscosity modifier, it stops products from separating and gives them a smoother slip. It also improves freeze-thaw stability, so your serum doesn't split if it's been sitting in a cold bathroom or a warm car.
It has an excellent safety record. The CIR Expert Panel concluded that propylene glycol is safe for use in cosmetics at current use levels, describing it as generally non-toxic and non-carcinogenic, with clinical studies showing an absence of dermal sensitisation at use concentrations. If you've seen scare headlines calling it "antifreeze," that's technically true of industrial-grade propylene glycol — but the cosmetic and food grades are a different, highly purified specification, and the comparison isn't a meaningful toxicological one.
Is It Safe for Everyone?
For the vast majority of people, yes. That said, honesty matters more than comfort here:
- Irritation is possible. Propylene glycol is a recognised, if uncommon, irritant and contact allergen. Reactions are more likely at high concentrations (above 50%) or on already-damaged, compromised skin. Estimates of true allergy in the general population sit around 1–2%.
- If you have eczema or a damaged barrier, you may find glycol-heavy formulas sting. Patch-test anything new on your inner forearm for 48 hours.
- Regulation. In the UK, cosmetics must comply with the EU Cosmetics Regulation (retained in UK law post-Brexit). Propylene glycol is permitted without a concentration limit for adults, though its use is restricted in products intended for children under three.
- If you suspect a reaction, stop using the product and speak to a pharmacist, GP or dermatologist rather than self-diagnosing.
For context, propylene glycol has a low comedogenicity rating (0) and low irritancy rating in standard ingredient assessments — meaning it's unlikely to clog pores at typical concentrations.
Which REFORM Skincare Products Contain Propylene Glycol?
REFORM Skincare is a doctor-led, cosmeceutical range formulated with high percentages of antioxidants and acids. Propylene Glycol appears in several of their products, and — importantly — the brand lists it openly on its own product pages rather than burying it.
The clearest confirmed inclusion is the brand's hero product:
HYAL • Vitamin C + E Serum — This is REFORM's flagship antioxidant serum, built around vitamin C, vitamin E, ferulic acid and hyaluronic acid. Propylene glycol appears third on the INCI list, after aqua and ascorbic acid, placing it in a relatively high concentration. REFORM describes it on their own site as "a hydrating solvent that improves ingredient delivery while helping maintain skin hydration" — which is exactly the dual role described above. The full ingredient list is documented on Incidecoder, where it is also classified as a moisturiser/humectant and solvent with an irritancy rating of 0.
That same penetration-enhancing function is precisely what you want in a vitamin C serum. Vitamin C is notoriously difficult to stabilise and deliver through the skin barrier; pairing it with propylene glycol and ethoxydiglycol is a deliberate formulation choice, not a filler.
Where to check for yourself. REFORM's range continues to evolve — new launches include the Skin Barrier Repair Cream and an SPF 50+ Invisible Mist Spray, and formulations can be updated. Rather than relying on a list that may age, use this rule: if a product is an aqueous serum or gel with a tricky active, check the label. The most likely candidates in the current REFORM line are:
| Product type | Where propylene glycol typically appears |
|---|---|
| Vitamin C and antioxidant serums | Very common — solvent and delivery agent |
| Gel-based treatments (Phyto Botanical Gel, Vitamin B5 Gel) | Common — texture and hydration |
| Lightweight moisturisers | Variable — humectant role |
| Creams rich in oils and butters | Less common — oil phase does the work |
The practical step is simple: each REFORM product page lists its ingredients, and Propylene Glycol will appear under that exact name if present. If your skin is sensitive, compare the labels before you buy — and if you're reacting to a product, look at the full formula rather than singling out one ingredient.
The Bottom Line
Propylene Glycol is one of the most useful workhorses in modern skincare. It hydrates, it dissolves, it stabilises, and — most valuably — it helps the expensive actives in your serum actually reach the skin. Its safety profile is well established and its regulatory status in the UK is straightforward, with irritation confined largely to high concentrations and compromised skin.
If you want to see it in action, REFORM's HYAL • Vitamin C + E Serum is the clearest example in the range — and a good illustration of why a "boring" ingredient is often the one making the hero ingredient work.
