Menthol feels cold because it switches on TRPM8, the nerve receptor that detects cool temperatures. The effect is a sensory trick: menthol does not lower the temperature of the mouth at all.
What it is¶
Menthol is a monoterpene alcohol — a ten-carbon molecule of the kind that makes up much of the aroma of herbs (see aroma-compounds). At room temperature it forms clear, needle-like crystals that melt a little above 40 °C. It is the dominant component of the essential oil of peppermint (Mentha × piperita) and of corn mint (Mentha arvensis), which is the main commercial source of natural menthol.
Not every mint is minty in this sense. Spearmint (Mentha spicata), the mint of mint sauce, mojitos and most British gardens, contains little menthol; its characteristic smell comes from (R)-carvone. That is why spearmint smells sweet and green and does not produce the icy blast of peppermint.
Menthol exists in several mirror-image and structural forms. The natural one, (−)-menthol, has the strongest cooling effect and the familiar clean smell; synthetic menthol is made both in this form and as a mixture.
How it works¶
🔬 The TRPM8 receptor
Nerve endings in the mouth and skin carry an ion channel called TRPM8 (transient receptor potential melastatin 8). It opens when temperatures fall below roughly 25 °C, becoming more active as things get colder, and signals "cool" to the brain. Menthol binds to TRPM8 and makes it open at normal body temperature, so the nerves report cold when nothing has been chilled.
TRPM8 was identified as the cold and menthol receptor in 2002 by two groups working independently, one in David Julius's laboratory and one in Ardem Patapoutian's. Both researchers later shared the 2021 Nobel Prize in Physiology or Medicine for work on temperature and touch receptors — the same family of discoveries that explains capsaicin's heat.
Menthol also makes TRPM8 more sensitive to real cold, which is why a glass of water after a peppermint tastes icy. At high concentrations it can activate other receptors too, including TRPA1 (the mustard oil receptor), which may contribute to the stinging, almost burning edge of very strong mints and menthol rubs.
Menthol and heat together¶
Capsaicin and menthol act on different receptors, so menthol does not cancel chilli heat in any chemical sense. It can, however, change how the combination feels: a strong cooling signal competes for attention with the burn. Mint is a traditional partner for hot food across South Asia and the Middle East — mint raita, green-chutney, mint tea after a meal — though much of the relief there comes from yoghurt and time rather than from menthol.
Other cooling compounds¶
Menthol is not the only molecule that feels cold.
| Compound | Where it occurs | Notes |
|---|---|---|
| Menthol | Peppermint, corn mint | The classic; strong smell |
| 1,8-cineole (eucalyptol) | Eucalyptus, bay, rosemary, cardamom | Fresh, camphorous; weak TRPM8 activator |
| Camphor | Some basils, rosemary, black-cardamom | Cooling and warming at once; toxic in quantity |
| Synthetic coolants (e.g. WS-3, WS-23) | Chewing gum, sweets, toothpaste | Developed to give cooling with little or no smell |
The synthetic "WS" coolants were developed in the 1970s by researchers at the razor maker Wilkinson Sword, hence the initials. They are now widely used in confectionery and oral care, where the smell of menthol would be unwanted.
Cardamom's cineole partly explains its reputation as a refreshing spice, and why a pod chewed after a meal feels cleansing.
In the kitchen¶
Menthol's properties shape how mint behaves in cooking.
- It is volatile. Long cooking drives menthol and the other aroma compounds off. Add fresh peppermint at the end, or use it raw.
- It is fat- and alcohol-soluble. Menthol dissolves readily in chocolate, cream and spirits, which is why mint chocolate and crème de menthe work so well and why peppermint oil is best added to a fat rather than water. It dissolves only slightly in water, so mint tea extracts it slowly.
- A little goes a long way. Peppermint essential oil is very concentrated; a drop or two flavours a whole batch of icing. It should never be substituted spoon for spoon for extracts.
💡 Which mint to use
For savoury cooking — mint sauce, salads, lamb, Vietnamese herb plates — use spearmint. Peppermint's menthol reads as toothpaste in savoury food. Keep peppermint for tea, chocolate and sweets.
Safety¶
Menthol is safe in culinary amounts. Concentrated peppermint oil is a different matter: it can irritate skin and mucous membranes, should be kept away from the faces of babies and young children, and is not a cooking ingredient in its undiluted form except by the drop.