Menthol

[Nitack]

So, I have recently been intrigued by the properties of menthol, the active ingredient in mint that gives it that "cool" feeling. Here is the wikipedia section that deals with this effect. Actually, here is the old form, I removed a sentence that was not factually supported by the abstract it linked to. That sentence is in bold. I have linked to the article.

Menthol's ability to chemically trigger the cold-sensitive TRPM8 receptors in the skin is responsible for the well known cooling sensation that it provokes when inhaled, eaten, or applied to the skin. Menthol does not cause an actual drop in temperature.[1] In this sense it is similar to capsaicin, the chemical responsible for the spiciness of hot peppers (which stimulates heat sensors, also without causing an actual rise in temperature).

I actually started researching menthol when I observed a very real temperature difference because of it.

Background: My mother in law is one of those people who only buys organic produce and thinks that modern medicine is all wrong. She tries to treat everything with oils and defusers and rails against anything with "chemicals" in them. She is right on some counts, I know that, organic produce is better and some times there are much better options that are "natural". One of the things she is right about is deodorant. My wife made me try this all natural deodorant and the active ingredient and fragrance agent is mint. It works very well, better than my old Degree, highly recommended.

So, I began noticing the very obvious cool feeling immediately upon use. I was under the impression that this was, as the wiki article stated, only a reaction by the cold receptors in my skin. No actual temperature change. However, a short time later I had an interesting observation. While driving with a short sleeve shirt on I noticed that when I touched the fabric with my hand (having no menthol on my hand at all), the fabric was cold. Noticeably cold to the touch. If the menthol was acting on the cold receptors in my armpit and simply tricking them into sensing cold, there should not have been any real temperature variation. I have thought about this and can narrow down the possible answers to the following:

1. The menthol is actually a conductor of heat and helped to sap heat away from my body. So, while driving, with the air flowing into the area of my body that was covered with the mint deodorant, the menthol transferred the heat from my body to the passing air very quickly.
2. The menthol causes my body to send less of the produced heat to the effected area.
3. The menthol had vaporized and interacted with my hand when I touched the fabric.
4. The fabric was simply cooled by air flowing into my shirt and the menthol was just a coincidence.

I believe option one to be the most likely due to my observation. I believe option two to be unlikely, however can not discount it entirely with out some serious medical testing. I believe option three to be unlikely but it is at least possible as far as I see so can not be discounted. I do not believe option four to be true, as other parts of my shirt that were not near my armpit were no where near as cold.

The next step I suppose is to start testing. If I can show a measurable difference in temperature, obviously using measurement equipment for the sake of objectivity and not just it feeling cold from my touching it, then it has indeed conducted the heat away from my body. I will first use two identical thermometers and coat one with either mint oil, mineral ice stuff, or my deodorant. Then I will position them both in front of a fan in order to see if one thermometer loses more heat than the other. If this test proves negative then there is still an additional test to be performed, to see if menthol only conducts heat when reacting with human skin. The test here would be to put deodorant under one arm, the other with out, and sit with my arms in the air in front of a fan. After a sufficient time had passed, place thermometers in both armpits (never to be used for oral measurement again ), lower both arms and see what the temperature reads. If that test is also negative, I can see that my initial observation was some how flawed and that menthol is not in fact a conductor of heat and that some other explanation accounted for the observed effect.

What are your thoughts?

[Nitack]

So I found some interesting information almost immediately after posting this. It does not answer my questions, but possibly takes the answer into a whole new direction. I have bolded the interesting part.

Menthol and nicotine oppositely modulate body temperature in the rat

David N. Ruskina, Corresponding Author Contact Information, E-mail The Corresponding Author, Rene Anandb and Gerald J. LaHostea
aDepartment of Psychology, University of New Orleans, New Orleans, Louisiana, USA bNeuroscience Center of Excellence, Louisiana State University Health Sciences Center, New Orleans, Louisiana, USA

Abstract

Menthol is a prominent additive in many tobacco products. To investigate possible interactions with nicotine, (−)-menthol (200 or 400 mg/kg) and (−)-nicotine (0.5 mg/kg) were injected subcutaneously in rats, and body temperature, which is modulated by brain nicotinic acetylcholine receptors, was measured. Nicotine caused robust (− 1.6 °C) hypothermia, the magnitude and time course of which was not altered by menthol pretreatment. Menthol alone produced mild (0.4–0.8 °C) hyperthermia, which was not secondary to locomotor activation. Nicotine and menthol influence body temperature independently and oppositely; menthol does not appear to influence the function of the central nicotinic receptors that control body temperature.

Keywords: Nicotinic acetylcholine receptor; α4 subunit; Core temperature; Hypothermia

Menthol actually caused the body of the rat to produce more heat. So what if menthol does not actually conduct heat away from the body, or activate the receptors responsible for sensing cold, but instead causes localized heat production to increase slightly, giving the feeling of cold as that localized heat is lost to the surrounding atmosphere. I am not sure that would match up with my first observation of the cold fabric though.

Getting more confused by the minute...

[freeztar]

This is an interesting question and I like how you are applying the scientific method.

Have you run your experiments yet?

[Moontanman]

Does the medium the menthol (water, alcohol) is dissolved in evaporate and cause the temperature decrease?

[Nitack]

Originally Posted by Moontanman

Does the medium the menthol (water, alcohol) is dissolved in evaporate and cause the temperature decrease?

In the case of mint oil or mineral ice I would say that is distinctly possible considering both contain water at least and I know the mineral ice contains alcohol. In the case of the deodorant, where the effect was first observed, no.

AromaGuard Mountain Mint - Deodorant

Ingredients listed below:
Cocos Nucifera (Coconut) oil, White Beeswax, Pure Vegetable Esters, Zinc Oxide, Tocopherols (Vitamin E), Syzygium Aromaticum (Clove)†, Citrus Medica Limonum (Lemon) Fruit Oil, Mentha Piperita (Peppermint)†, Rosmarinus Officinalis (Rosemary), Eucalyptus Radiata† Leaf Oil, and Abies Concolor Oil.

[freeztar]

From everything I'm seeing while researching this, menthol only activates cold receptors which produces thermosensation.

Apparently the CMR1 receptor is responsible.

Peppermint - Chempedia

So, I would vote for 3 or 4 on your list.

[Nitack]

Originally Posted by freeztar

From everything I'm seeing while researching this, menthol only activates cold receptors which produces thermosensation.

Apparently the CMR1 receptor is responsible.

Peppermint - Chempedia

So, I would vote for 3 or 4 on your list.

But, the question gets further complicated with the study I cited in my second post doesn't it? Could the mild hyperthermia be the body intentionally producing more heat in reaction to the perceived cold? Or, could the percieved cold be a reaction to the body producing more heat and the air/tissue/area/atmosphere around the area of exposure seeming cold by comparison.

[modest]

Originally Posted by Nitack

1. The menthol is actually a conductor of heat and helped to sap heat away from my body. So, while driving, with the air flowing into the area of my body that was covered with the mint deodorant, the menthol transferred the heat from my body to the passing air very quickly.
2. The menthol causes my body to send less of the produced heat to the effected area.
3. The menthol had vaporized and interacted with my hand when I touched the fabric.
4. The fabric was simply cooled by air flowing into my shirt and the menthol was just a coincidence.

Deodorant would make a cold spot just by being a barrier between your shirt and body I would think. Your shirt would naturally be heated by your body:



If that particular deodorant were a good insulator of heat then there would be a cold spot on your shirt where your body is heating the shirt less. That would, at least, be a possibility.

~modest

[Mercedes Benzene]

Menthol is NOT physically cold. Cold is just a perception when something wicks away energy from our bodies. For something to feel cool, it either has to (a) easily absorb large amounts of energy, or (b) evaporate readily, so as to wick energy away quickly. Obviously, both of those conditions may apply.

Organic liquids such as acetone or alcohol feel extremely cool on our body because they absorb a lot of energy, and then evaporate, carrying that energy away from us.
Ethanol has a vapor pressure or 44.6 mmHg at 20 degrees C, so it evaporates readily, and therefore feels very cool. Menthol, on the other hand, has a vapor pressure of 0.8 mmHg at the same temperature. It does not evaporate easily, and does not absorb energy readily. Water's vapor pressure, by comparison to the two, is about 17.6 mm Hg.

Many studies, however, have proven that menthol interacts with the TRPM8 receptors in the skin, and so it feels cold, when in reality, there is no exchange of heat energy.

[freeztar]

Originally Posted by Mercedes Benzene

Many studies, however, have proven that menthol interacts with the TRPM8 receptors in the skin, and so it feels cold, when in reality, there is no exchange of heat energy.

Can you link to some of these studies?

I tried searching along those lines and found many articles that dealt with the different skin receptors and how the clacium-ion channel is enabled which causes pores to open in the same manner that cold temperature causes them to open. I guess the big question in my mind is: Does the skin's reaction to menthol, similar to the reaction to 'cold', invoke the same physiological response (heat transfer)?