How menthol keeps the world cool
The distinct cooling effect on the skin and mucous membranes has made menthol a popular ingredient in many products, from toothpaste and mouthwashes to skin creams and pharmaceuticals. But what’s the secret behind this remarkable cooling effect?
In the early 1950s, German physiologist Herbert Hensel and the Swedish neurophysiologist Yngve Zotterman conducted a series of seminal studies, showing that menthol elicited its cooling sensation by increasing the threshold temperature for activation of cold receptors. The two scientists hypothesized that menthol exerted its actions on “an enzyme” that was involved in the activation of these nerves. It took until 2002, half a century, for Hensel and Zotterman’s hypothesis to be validated.
In 2002, a group of researchers could show that menthol selectively activates the cold receptor Transient Receptor Potential Melastatin, TRPM8, today also called the Menthol receptor, which is located on the nerve endings of the skin.
TRPM8 is an ion channel and was the first cold-activated ion channel to be identified in these experiments in the early 2000s, and it established the general role for TRP ion channels in thermosensation.
TRPM8 is activated by cooler temperatures (around below 25°C) and chemical agonists such as menthol. Chemical agonists are chemical substances that bind to certain receptors on cells and activate them, causing a biological reaction. When menthol binds to TRPM8, it causes a change in the flow of ions across the cell membrane, resulting in depolarization of the nerve cell.
This depolarization causes us to feel cold, even though there is no actual change in temperature. This ability to produce a cool sensation without actual cooling makes menthol particularly useful in products that aim to provide rapid relief from heat or pain.
Menthol is also widely used to treat nasal congestion, but studies have shown that menthol has no effect on the opening of blocked or restricted nasal airways. Similarly to the cooling effect one the skin, menthol doesn’t unblock your nose, it just makes you think it does. Stimulating TRPM8 receptors in the nose, it creates the sensation of increased airflow.
Since menthol has been shown to stimulate these cold receptors in the mouth and nose, scientists have also published papers with the hypothesis that menthol, may also influence thirst, the drive to breathe, as well as arousal.
Studies like these show that menthol is not just one of the most popular and versatile ingredients, but it keeps fascinating scientists (and consumers alike) with its distinctive cooling properties.