Menthol Is in Six of Our Products and Doesn't Cool Anything. It Opens a Cold Receptor.

Rinse a scalp scaler out and your head stays cold for the next ten minutes. The water was warm. The room did not change temperature. Something told your brain cold anyway.

That signal is not a measurement. It is a lock being picked, and the thing picking it is menthol.

We counted our own shelf for this one, line by line, rather than trusting the count we made in July. Menthol appears in six of the fifty-six products we sell. It does something genuinely interesting, and almost none of what it does involves removing heat from your skin.

What menthol does is open a channel

In 2002 two labs published the same discovery within weeks of each other. David McKemy's group in Nature called it a cold receptor and pointed out that TRP channels do general thermosensation work. Andrea Peier's group in Cell put it in the title: a TRP channel that senses cold stimuli and menthol.

The channel is TRPM8. It sits in the membrane of sensory neurons and it opens when the temperature around it drops, which is how you know a doorknob is cold. Menthol opens the same channel chemically. The neuron cannot tell the difference between a molecule prying the gate open and actual cold prying it open, so it sends the same message either way.

Which is why the sensation is so convincing and so useless as information. TRPM8 reports cold. Your skin is not cold.

This also explains the part people find annoying about menthol products, which is that a cold shower afterwards feels absurd. The channel is already open. Real cold arrives at a receptor that is halfway through reporting cold and the two stack.

What the thermometer says

Here is where we have to be careful, because the popular version of this article says menthol does not cool your skin at all, and that overstates what the studies found.

Lasanen and colleagues tested whether the amount of menthol in a topical cold gel changed how much the skin actually cooled. Ten people. The answer in the title of the paper is that menthol concentration does not have a significant effect on skin cooling, meaning the gel cooled and the menthol in it was not what did the cooling. A wet gel evaporating off skin removes heat whether or not there is menthol in it.

Gillis and colleagues went at the dose question twice. Sixteen people in the first study, thirteen men in the second, looking at how menthol dose and how much body surface you cover change temperature regulation and perception. Perception moves. The regulatory picture is more complicated than the sensation is.

So the honest statement is narrower than the popular one. The cold you feel from menthol is not produced by heat leaving your skin. Whether your skin temperature falls at all, and by how much, depends on what the menthol is dissolved in and which study you read.

Every one of these studies is small. Ten, thirteen, sixteen, twenty people. We looked for a large randomised trial of topical menthol and skin temperature and did not find one.

Six products, and only one of them calls it cooling

Here is what our recount actually turned up.

The row that matters is the last one. In the hair tonic, menthol is not filed as a sensory ingredient at all. It is filed under a Korean functional-cosmetics category, sitting alongside dexpanthenol and salicylic acid as an anti-hairloss active. That is not our invention. It is how the ingredient is positioned in that product class in Korea, and it means the same molecule is doing sensory duty in five products and claiming a functional benefit in the sixth.

We also grade it inconsistently. Five mid, one low, same substance. The low sits in the dye shampoo, where menthol is a rounding error next to two high-risk oxidative dyes, and a grading system that lets context leak into an ingredient-level score is a grading system with a bug in it.

Camphor turns up once, in the foot cream, also graded mid, also filed as cooling. Menthyl lactate, the gentler synthetic cooler that shows up constantly in Western aftershave and lip products, appears in our catalogue zero times.

Mint arrives under four other names

Searching an ingredient list for the word "Menthol" undercounts the mint in your bathroom, and our own shelf is a decent demonstration.

Four more products carry Mentha-genus material without the word menthol anywhere near it. A pore strip carries peppermint oil and peppermint extract. A body pad carries spearmint extract. A cleansing foam carries Mentha arvensis leaf powder, which we filed under texture, because in that product it is a physical particle rather than a sensory ingredient. The scalp scaler carries Mentha arvensis leaf oil and peppermint oil on top of its declared menthol.

Count products rather than lines and the total goes from six to nine out of fifty-six.

Peppermint oil is meaningfully menthol-bearing. Spearmint is mostly not, and leaf powder is a different proposition again. We are not going to flatten those into one number and tell you nine products will make you feel cold, because they will not. The point is narrower: if you are avoiding menthol because it stings broken skin or because you have reacted to it, the word you are searching for is not the only word that matters.

Where the evidence stops

Blood flow is the part we cannot resolve, and it is the part most product copy is quietly confident about.

Hunter and colleagues looked at what a topical menthol cooling gel does to soft tissue thermodynamics and to arterial and cutaneous blood flow at rest, in twenty people. Botonis and colleagues looked at menthol on skin during prolonged immersion in cool and cold water. Read across this literature and the direction of the blood-flow response is not settled. Some designs point one way and some point the other, and the vehicles, the doses and the body sites are all different, which is exactly the situation where you should not pick the result you like.

So we do not know whether the menthol in our scalp products constricts or dilates the vessels underneath, and neither does anyone selling you a scalp tonic on the strength of increased circulation.

One more piece of precision while we are here. The scalp scaler also contains terephthalylidene dicamphor sulfonic acid, which has camphor in the name and nothing to do with cooling. We grade it as an antioxidant, low risk, and that is what it is doing there.

What our screening found

What to do with this at the shelf is simple enough. If you like the sensation, buy the sensation, and understand you are buying a signal rather than a temperature. If menthol stings you, search the list for peppermint and Mentha as well as for menthol. And if a scalp product is selling you improved circulation, that is the claim to be sceptical about, because the literature underneath it does not agree with itself yet.

We have written before about what hair-loss shampoos can and cannot do, about the salicylic acid that turns up alongside menthol in most of these formulas, and about the ten ingredients we flag most often. How the grading works, bug and all, is on our screening method page and our awards page.