Cooling Agents in Personal Care & Cosmetics: Formulation Insights

The cooling sensation in a post-shave balm, a lip gloss, a foot cream, or a sunscreen is rarely accidental. It is achieved through precise dosing of cooling agents — a class of ingredients that activate the TRPM8 cold receptor in the skin with varying onset times, intensities, and durations.

For cosmetic formulators, the choice between menthol, WS-3, WS-23, menthyl lactate, and other cooling agents is not a simple matter of "which is strongest." It is a decision that affects sensory profile, formulation stability, regulatory labelling, and cost per kilogram of finished product.

Understanding Cooling Agents: Beyond Menthol

Menthol — The Benchmark

Menthol remains the reference standard against which all other cooling agents are measured. It activates TRPM8 at low concentrations (threshold around 0.1–1 ppm in solution) and produces a characteristic cooling sensation that most consumers recognize.

However, menthol has properties that complicate cosmetic formulation:

• Volatility: Menthol sublimes at room temperature. In open or semi-permeable packaging, it can migrate, leaving the product with reduced cooling over time.
• Low melting point (41–44 °C): In hot-processed formulations (lipsticks, balms, sunscreens), menthol can melt during production and recrystallize unevenly upon cooling.
• Odour: Menthol has a strong minty, penetrating odour. In fragrance-sensitive formulations or products where a specific scent profile is desired, menthol's odour can be a limitation.
• Irritation potential: Above certain concentrations, menthol causes a burning or stinging sensation rather than a cooling one. The threshold is formulation-dependent.

Next-Generation Cooling Agents

WS-23 has become the preferred agent in many cosmetic applications because it provides strong, clean cooling with essentially no odour and minimal irritation. The onset is rapid, and the duration at 0.2% in a gel formulation is comparable to 1% menthol.

Formulation by Product Category

After-Shave Balms and Lotions

After-shave products are one of the most demanding applications for cooling agents. The skin is freshly shaved (compromised barrier, micro-cuts) and highly sensitive. Formulators need cooling without stinging.

Recommended approach: WS-23 at 0.1–0.2% combined with a low level of menthol (0.05–0.1%) for the characteristic cooling freshness that consumers associate with post-shave products. Avoid menthol alone above 0.2% — the sting risk is significant.

The base formulation should include skin-soothing agents (panthenol, aloe, allantoin) to offset the sensory impact of cooling. Cooling agents are irritating at high concentrations, not because they are inherently toxic, but because the TRPM8 activation pathway at high intensities triggers nociceptor co-activation.

Sunscreens

Sunscreen formulations present a unique challenge. The combination of UV filters (particularly inorganic filters like zinc oxide and titanium dioxide), emollients, and film formers creates a thick, often occlusive vehicle that can suppress the perception of cooling agents. Additionally, the sunscreen film must remain intact for SPF claims — adding a volatile cooling agent that migrates within the film can disrupt UV protection.

Recommendation: Use menthyl lactate at 0.5–1.0% or WS-3 at 0.2–0.3%. These have lower volatility than menthol and are less likely to migrate within the sunscreen film. Avoid menthol in high-SPF formulations — the volatility is simply too high, and stability data consistently shows >40% loss of menthol over 3 months at 40 °C.

Lip Products (Balm, Gloss, Plumper)

Lip formulations require cooling agents that do not crystallize at the surface, do not produce an unpleasant taste, and provide an immediate sensation that consumers interpret as "plumping" or refreshing.

Menthyl lactate is the most versatile choice for lip products. It is a solid (MP 42–47 °C, close to body temperature) that melts on application, providing a gradual cooling release that consumers describe as "lingering." Typical levels: 0.5–1.5% in lip balms, 0.3–0.8% in lip glosses.

Menthol can be used at 0.1–0.5% but watch for crystallization (blooming) on the lipstick surface during storage. The addition of a small amount of a liquid cooling agent like menthoxypropanediol can suppress recrystallization.

Foot Creams and Sports Gels

Foot care is the category where aggressive cooling is expected. High concentrations of WS-23 (0.3–0.5%) or menthol (2–5%) are common. The thicker skin on the feet tolerates higher levels.

Sports gels and muscle rubs follow the same pattern that pharmaceutical topical analgesics do — menthol at 3–10%, often combined with methyl salicylate or camphor. In this category, the cooling sensation communicates "active ingredient" to the consumer, so higher levels are functionally and perceptually appropriate.

Stability and Compatibility

Chemical Stability

Most cooling agents are chemically stable in the pH range 4–8, which covers the vast majority of cosmetic formulations. Outside this range — for example, in high-pH soap formulations — hydrolysis of ester-type coolants (menthyl lactate) can occur. If your product has a pH above 8.5, stick with amide-type coolants (WS-3, WS-23).

Physical Stability

The biggest formulation failure mode with cooling agents is recrystallization. This happens when:

• The cooling agent exceeds its solubility limit in the oil phase
• The formulation is stored at low temperature (e.g., winter shipping)
• The product is anhydrous and the coolant supersaturates during cooling from the melt

Prevention: Determine the solubility limit of each cooling agent in the specific oil phase of your formulation. Do not rely on literature values — they vary with the triglyceride profile, ester composition, and other oil-phase ingredients. A pre-formulation solubility study at 4 °C, 25 °C, and 40 °C is cheap insurance against a crystallization complaint.

Sensory Stability Over Time

Cooling agents at very low use levels can appear to fade because they partition into packaging materials. WS-23 has particularly low affinity for polypropylene and can be used with standard cosmetic packaging without significant loss. Menthol has a higher affinity for polyolefins and requires aluminium-lined tubes or jars for long-term retention.

Regulatory Considerations

EU Cosmetics Regulation (EC) No 1223/2009

Most cooling agents used in cosmetics are not specifically restricted. Menthol is listed in the CosIng database and is permitted at concentrations considered safe by the SCCS. WS-3 and WS-23 are also CosIng-listed. Menthyl lactate is listed as a skin-conditioning agent.

The key regulatory consideration is labelling. The INCI name must be used in the ingredient listing. Cooling agents are not currently flagged as allergens in the EU Cosmetics Regulation (unlike fragrance allergens such as limonene, linalool), but customer expectations in Europe increasingly favour products without synthetic cooling agents.

US FDA (FD&C Act)

Cooling agents are classified as cosmetic ingredients and are not subject to FDA pre-market approval. However, if a cooling agent provides a therapeutic benefit (e.g., "relieves muscle pain"), the product becomes a drug and requires regulatory clearance. This distinction matters for marketing claims.

Halal and Kosher Certification

Menthol from natural sources (Mentha species) is generally halal and kosher certified. Synthetic cooling agents require verification — some synthetic pathways use ethanol or other solvents that may affect certification status.

Procurement Tips

1. Request the COA with sensory characterization: The GC assay tells you purity. The sensory panel data (cooling intensity vs. menthol reference) tells you whether the batch performs as expected.

2. Verify solvent residues: Some cooling agents are spray-dried or recrystallized using solvents. Request residual solvent data, particularly for WS-3 and WS-23.

3. Ask about particle size for solid coolants: Menthyl lactate and WS-3 are often supplied as powders. If your process involves direct addition to a cold-mix phase, micronized grades (<50 µm) disperse better.

4. Check the melting point specification: A menthyl lactate batch with a depressed melting point indicates contamination with menthol or lactic acid — both of which change the cooling profile.

Frequently Asked Questions