Propylene Carbonate in Skin Care: Safety and Use Levels

By RawSource Sourcing Desk, Commercial & Sourcing Desk · About RawSource

A formulator hands procurement a bill of materials that lists “PC” at 8%. Someone reads it as propylene glycol, the cheaper glycol a few rows down the catalog, and orders a drum. The pigment grind for a tinted night cream will not disperse, a pilot batch goes grainy, and the lot is scrapped. The two materials share three letters and a “propylene,” and nothing else that matters to the formula.

Propylene carbonate earns its place in skin care for one reason: it dissolves and carries things that water and the common glycols cannot. That makes it a workhorse in color cosmetics, sunscreens, and pigment dispersions. It also carries a specific safety profile and a clear concentration ceiling that a procurement team needs to read before, not after, the first shipment.

This explainer walks the chemistry, the CIR safety conclusion, the real use levels, then the grade question the way a sourcing desk has to read them, with the numbers and the named regulations you can put in front of QC and regulatory affairs at the same time.

Key takeaways

• Propylene carbonate (CAS 108-32-7) is a polar aprotic solvent and carrier, not a humectant like propylene glycol. With zero hydrogen-bond donors and three acceptors, it wets pigments and dissolves actives that water and glycols leave behind.
• The CIR Expert Panel’s 2025 amended report concluded propylene carbonate is safe in cosmetics as used, with one condition: formulated to be non-irritating. Undiluted material is a GHS H319 eye irritant.
• It appears in 882 reported cosmetic formulations and is used at up to 17.9% in leave-on night skin-care preparations, per the 2022 Council concentration survey.
• It barely penetrates skin: 0.7 g/m2 per hour in a dermal assay, against 24 for water. The FDA lists it as a topical-ointment inactive ingredient up to 3,000 mg maximum daily exposure.
• Grade decides fitness for use. Specify the assay floor and a per-lot CoA before the first quote.

What is propylene carbonate, and why does “polar aprotic” matter?

Propylene carbonate is the cyclic carbonate ester of propylene glycol, IUPAC name 4-methyl-1,3-dioxolan-2-one, molecular formula C4H6O3, molecular weight 102.09. It is a colorless, odorless liquid at room temperature (PubChem CID 7924). The CIR identifies its cosmetic functions as solvent and viscosity-decreasing agent, the same two roles the catalog records under INCI name PROPYLENE CARBONATE.

The phrase that decides where it goes in a formula is “polar aprotic.” The molecule has a strong dipole but no hydrogen-bond donor, with zero donors and three acceptors on the PubChem record. That combination lets it dissolve polar solids and many organics while staying water-soluble, at roughly 175 g/L at 25 degrees C. A humectant such as propylene glycol holds water against the skin. Propylene carbonate does a different job: it carries and disperses the material that has to go into the product but will not dissolve on its own.

In skin care that translates to three recurring uses: wetting and grinding pigments in color cosmetics, dissolving UV filters and other actives, and thinning a system without the tack a glycol can leave. The low skin penetration, covered below, is part of why formulators reach for it as a carrier instead of a delivery agent.

Is propylene carbonate safe in skin care?

The short answer carries a condition. The Cosmetic Ingredient Review (CIR) Expert Panel for Cosmetic Ingredient Safety concluded that propylene carbonate “is safe in cosmetics in the present practices of use and concentration described in this safety assessment when formulated to be non-irritating.” That wording comes from the CIR amended safety assessment, published in 2025, which re-opened a record that traces back to an original 1987 report and was re-affirmed in 2006 and 2012.

The “non-irritating” condition is not boilerplate. The pure liquid is a GHS H319 eye irritant on the PubChem record, and the CIR review noted that undiluted propylene carbonate produced minimal to moderate ocular irritation in rabbits. Diluted to use levels the picture changes: a 20% solution was non-sensitizing and ranged from non-irritating to moderately irritating on human skin in the data the Panel reviewed. The Panel re-opened the assessment at its March 2023 meeting precisely because frequency and concentration of use had climbed, then confirmed the safe-as-used conclusion with the non-irritating caveat attached.

Two more data points shape the risk read. Propylene carbonate is poorly absorbed through skin: a dermal penetration assay on human skin measured a permeability rate of 0.7 g/m2 per hour, against 24 g/m2 per hour for water, and the reviewers concluded it is not readily absorbed. And the FDA already accepts it in drug products, listing propylene carbonate as an inactive ingredient in topical ointment drug products up to a maximum daily exposure dose of 3,000 mg. For the sourcing read across the broader pharmaceuticals and beauty and personal care lines, that combination, low penetration plus an existing FDA inactive-ingredient record, is the reason it clears formulation review with minimal friction.

The genuine trade-off: the same property that makes it a strong carrier, a high-dipole liquid that wets almost anything, is what makes neat product an eye irritant. Handling controls (splash goggles, the H319 precautionary statements) apply to the drum, not to the finished cosmetic.

Where is it used, and at what level?

Use is concentrated in leave-on products. The 2023 VCRP survey reported propylene carbonate in 882 cosmetic formulations, split 874 leave-on to 8 rinse-off, so it is overwhelmingly a stay-on-skin ingredient rather than a wash-off one. The 2022 concentration-of-use survey conducted by the Council found a maximum reported level of 17.9% in leave-on formulations, in the night skin-care category (non-spray).

That 17.9% ceiling is a survey maximum, not a typical dose. Most uses sit far lower, where the material acts as a pigment wetting agent or a co-solvent at a few percent. The high end shows up where the carrier is doing heavy lifting, dispersing a large pigment load or dissolving a stubborn active in an anhydrous night treatment.

For a buyer, the practical signal is duration of contact. Because the volume is leave-on, the non-irritating condition from the CIR is the controlling design constraint: the finished formula has to be irritation-tested at its real use level, not assumed safe because the molecule cleared review.

Propylene carbonate or propylene glycol: which does your formula need?

This is the question behind the scrapped-batch story at the top, and it is worth a direct comparison because the two get confused on spec sheets and in purchasing. They are different molecules with different jobs. Propylene glycol is a diol humectant that holds moisture; propylene carbonate is a cyclic ester that acts as a polar aprotic carrier. Substituting one for the other does not shift a formula slightly, it removes the function the formula was relying on.

If the formula needs to keep skin hydrated, that is a propylene glycol job, and the propylene glycol moisturizing write-up covers it. If the formula needs to wet a pigment or dissolve an active, that is propylene carbonate. The safety questions differ too. For the glycol side, see propylene glycol safety and environmental considerations; the oxygen-demand and grade issues there do not map onto the carbonate.

How is it regulated beyond cosmetics?

Propylene carbonate carries a clean cross-sector record that a regulatory-affairs reviewer will want on file, because cosmetic raw materials rarely live only under cosmetic rules. Three named federal references cover the most common adjacent uses.

For food-contact applications, the FDA permits propylene carbonate as a component of adhesives used in food packaging under 21 CFR 175.105. For agricultural and antimicrobial uses, residues from propylene carbonate as an inert or active ingredient in a pesticide formulation are exempt from a tolerance requirement under 40 CFR 180.950, when used per good agricultural or manufacturing practice. In the EU, the substance is REACH-registered under EC number 203-572-1.

The hazard communication is consistent across all of these: GHS signal word Warning, hazard statement H319 (causes serious eye irritation), with the precautionary statements P264, P280, P305+P351+P338, and P337+P317. There is no flammability flag at ambient conditions, since the flash point sits at 116 degrees C, well above the GHS cutoff for a flammable liquid. The decomposition note on the PubChem record is the one thermal caution: heated to decomposition, it emits acrid smoke and irritating fumes, which only matters at fire temperatures.

What should the purchase specification say?

Grade is the variable a buyer controls, and it is where most propylene carbonate problems start. The CAS number 108-32-7 covers material sold for electrochemistry (battery electrolytes), for general technical solvent use, and as a high-purity reagent. They are the same molecule at different assays and impurity ceilings, and a battery-grade lot is specified for water content and metal ions, not for skin contact.

For a cosmetic or topical program, four lines settle most of the risk. State the grade and assay floor. Require a Certificate of Analysis (CoA) per lot, with water content reported, since the material is hygroscopic and a wet lot drifts out of spec. Name the intended use so the supplier ships against a skin-contact specification rather than a technical one. And confirm the GHS documentation and Safety Data Sheet (SDS) match the lot. Buyers can review specifications and request a quote on the propylene carbonate product page, stating the grade and CoA fields up front.

Set those four lines before the first quote, and the formulation, QC, and regulatory reviews close on their own instead of stalling a launch over a grade no one wrote down.

Frequently asked questions

Is propylene carbonate the same as propylene glycol? No. They share a propylene root and both move other ingredients around a formula, but propylene carbonate is CAS 108-32-7, a cyclic carbonate ester (C4H6O3), while propylene glycol is CAS 57-55-6, a diol. Propylene carbonate is a polar aprotic solvent for pigments and actives; propylene glycol is a humectant. They are not interchangeable on a bill of materials.

Is propylene carbonate safe in skin care? The CIR Expert Panel concluded in its 2025 amended report that it is safe in cosmetics as used when formulated to be non-irritating. Undiluted propylene carbonate is a GHS H319 eye irritant and produced minimal to moderate ocular irritation in rabbits, but a 20% solution was non-sensitizing and ranged from non-irritating to moderately irritating on human skin.

How much propylene carbonate is used in cosmetics? Up to 17.9% in leave-on formulations, specifically night skin-care preparations that are not sprays, per the 2022 Council concentration-of-use survey. The 2023 VCRP survey reported 882 formulations using it, 874 leave-on and 8 rinse-off.

Does propylene carbonate penetrate the skin? Minimally. A dermal penetration assay on human skin measured a permeability rate of 0.7 g/m2 per hour, against 24 g/m2 per hour for water, and the reviewers concluded it is not readily absorbed through the skin.

What grade of propylene carbonate do I need for a cosmetic formula? Match the grade to the end use and document it. The same molecule, CAS 108-32-7, is sold as electrochemical, technical, and reagent grades that differ in assay and impurity limits. For skin-contact use, specify the assay floor and require a Certificate of Analysis (CoA) per lot.

Methodology: physical constants (boiling point, melting point, flash point, density, water solubility, GHS classification) are drawn from PubChem CID 7924. The safety conclusion, cosmetic functions, use frequency (882 formulations), maximum use concentration (17.9%), dermal-penetration rate, and FDA inactive-ingredient status come from the CIR amended safety assessment of propylene carbonate (2025). Regulatory references: 21 CFR 175.105 and 40 CFR 180.950. Confirm lot-specific values against the supplier CoA before specifying.

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Commercial & Sourcing Desk