Menthol: A small molecule full of minty magic!
Menthol is a natural substance that gives a cooling sensation and has a minty smell. It's a key ingredient in many products we use every day, like chocolate, chewing gum, and toothpaste.
If you like your breathe minty fresh, you likely have this molecule to thank! Menthol is a natural compound found in mint plants, though it can also be produced in a chemistry lab. Notably, menthol is one of the most important flavoring additives used today besides vanilla and citrus.
What is Menthol?
Chemically speaking, menthol is a cyclic monoterpene alcohol. It makes up a large share of the essential oil content of peppermint (Mentha x piperita, in the Lamiaceae plant family) and cornmint (Mentha candadensis). Menthol is the ingredient that gives certain plants, especially mint plants, their cool, minty taste and smell. It's not the only one, though; other compounds like menthone and isomenthone also contribute to the unique flavor and aroma. Originally, these plants were the only source of menthol, and they have a long history of being grown for medicinal uses, particularly in Japan. The first person to isolate menthol as a specific compound was a Dutch botanist named Gambius, who did so way back in 1771.
Commercial Uses of Menthol
It’s estimated that an incredible 32,000 metric tons of menthol is consumed each year! It is prominent in many tobacco products, including cigarettes and vapes. Roughly 25% of all cigarettes sold contain menthol. But, you can also find menthol in many common household products, such as:
chewing gum
candy
shampoo
toothpaste
soaps
cough drops
cosmetics
pharmaceuticals
One interesting use of menthol is that it helps some medicines penetrate the skin more effectively. As I described in my recent post on herbs for cold and flu season, menthol is also a key ingredient in chest balms (e.g., Vicks VapoRub) and steam inhalants that can ease congestion and aid in breathing.
Menthol’s Cooling Effect
Menthol is famous for giving you a cool feeling when you breathe it in, eat it, or put it on your skin. This happens because menthol triggers specific receptors that make your body think it's feeling cold. Studies have found that this cooling sensation can last for over an hour in most people tested. Interestingly, some research shows that menthol doesn't just make you feel cooler. In rats, a small amount of menthol actually made them seek out warmer places. In humans, some even reported feeling warmer after applying menthol, especially at higher temperatures. So, while it's mostly known for its cooling effects, menthol can sometimes have a warming effect too.
Pharmacology
Menthol has a number of interesting pharmacology properties. Here, I break down a few:
Analgesic (pain-relieving) Properties
Research has shown that menthol can affect how we feel pain. In some studies, applying menthol to the skin reduced sensitivity to both cold and heat, although these effects could vary based on factors like concentration. Interestingly, menthol seems to work by interacting with specific channels in nerve cells that are key to feeling pain. Not all forms of menthol have the same effect; some can actually make pain worse. Overall, menthol's effects are complex and can depend on many factors, including the specific kind used and how it's applied.
Antipruritic (anti-itch) Properties
Menthol has shown mixed results in reducing itchiness; some studies say it helps while others find it could irritate the skin more. It has also been shown to numb irritation in the mouth after repeated exposure.
Antitussive (against cough) Properties
Menthol is often an ingredient in cough remedies, and studies have shown it can reduce coughing to some extent. One study found that menthol reduced cough frequency by up to 56% in guinea pigs. In another study on children, inhaling menthol led to fewer coughs, although the improvement wasn't statistically significant compared to a placebo.
Antibacterial Properties
Menthol and peppermint oil have been found to have antibacterial properties, effective against various bacteria and even some antibiotic-resistant strains. These natural compounds can also combat respiratory pathogens when inhaled. The antibacterial effects are thought to result from the disruption of the bacteria's cell membrane. Despite these promising results, more research is needed to fully understand how menthol and peppermint oil work at the microscopic level.
Antifungal Properties
Studies have found that menthol can inhibit the growth of certain fungal strains, including some that spoil food or cause skin infections. The effectiveness of menthol varies depending on its concentration and form, with some studies noting that even the way a menthol molecule is shaped can impact its antifungal power. Peppermint oil vapors, which contain menthol, have also been effective in inhibiting fungal growth.
The Takeaway
Menthol and menthol-rich plants such as peppermint have been used for centuries in traditional medicine and has a wide range of applications today, from cosmetics and pharmaceuticals to food and tobacco. It's best known for creating a cooling sensation when applied to the skin or inhaled. Menthol can also improve the skin's absorption of other drugs, making it a useful ingredient in topical treatments. However, while research shows promise, much is still unknown about how menthol works and its potential for new applications. Overall, interest in menthol remains high, as indicated by the large number of patents and ongoing research into its various uses.
To learn more about menthol, check out papers on the subject like this or this one. In the meantime, you can follow my lead and enjoy a refreshing glass of hot peppermint tea in the evening as the cool weather sets in.
Yours in health, Dr. Quave
Cassandra L. Quave, Ph.D. is a scientist, author, speaker, podcast host, wife, mother, explorer, and professor at Emory University School of Medicine. She teaches college courses and leads a group of research scientists studying medicinal plants to find new life-saving drugs from nature. She hosts the Foodie Pharmacology podcast and writes the Nature’s Pharmacy newsletter to share the science behind natural medicines. To support her effort, consider a paid or founding subscription, with founding members receiving an autographed 1st edition hardcover copy of her book, The Plant Hunter.
Available in hardcover, paperback, audio, and e-book formats!
