Menthol is an organic compound made synthetically or obtained from corn mint, peppermint or other mint oils. It is a crystalline substance, clear or white in color, which is solid at room temperature and melts slightly above. Menthol has local anesthetic and counterirritant qualities, and it is widely used to relieve minor throat irritation. Menthol also acts as a weak kappa opioid receptor agonist.
Menthol’s ability to chemically trigger the cold-sensitive receptors in the skin is responsible for the well-known cooling sensation it provokes when inhaled, eaten, or applied to the skin. In this sense, it is similar tocapsaicin, the chemical responsible for the spiciness of hot chilis (which stimulates heat sensors, also without causing an actual change in temperature).
Menthol is widely used in dental care as a topical antibacterial agent, effective against several types of streptococci andlactobacilli.
Menthol is included in many products for a variety of reasons. These include:
- In nonprescription products for short-term relief of minor sore throat and minor mouth or throat irritation.
Examples: lip balms and cough medicines.
- As an antipruritic to reduce itching.
- As a topical analgesic, it is used to relieve minor aches and pains, such as muscle cramps, sprains, headaches and similar conditions, alone or combined with chemicals such as camphor, eucalyptus oil or capsaicin. In Europe, it tends to appear as a gel or a cream, while in the U.S., patches and body sleeves are very frequently used.
Examples: Tiger Balm, or IcyHot patches or knee/elbow sleeves.
- In decongestants for chest and sinuses (cream, patch or nose inhaler).
Examples: Vicks VapoRub, Mentholatum, vapoRem.
- In certain medications used to treat sunburns, as it provides a cooling sensation (then often associated with aloe).
- In aftershave products to relieve razor burn.
- As a smoking tobacco additive in some cigarette brands, for flavor, and to reduce throat and sinus irritation caused by smoking. Menthol also increases nicotine receptor density, increasing the addictive potential of tobacco products.
- Commonly used in oral hygiene products and bad-breath remedies, such as mouthwash, toothpaste, mouth and tongue-spray, and more generally as a food flavor agent; e.g., in chewing gum, candy.
- In a soda to be mixed with water it is used to obtain a very low alcohol drink or pure (brand Ricqlès which contains 80% alcohol in France); the alcohol is also used to alleviate nausea, in particular motion sickness, by pouring a few drops on a lump of sugar.
- As a pesticide against tracheal mites of honey bees.
- In perfumery, menthol is used to prepare menthyl esters to emphasize floral notes (especially rose).
- In first aid products such as “mineral ice” to produce a cooling effect as a substitute for real ice in the absence of water or electricity (pouch, body patch/sleeve or cream).
- In various patches ranging from fever-reducing patches applied to children’s foreheads to “foot patches” to relieve numerous ailments (the latter being much more frequent and elaborate in Asia, especially Japan: some varieties use “functional protrusions”, or small bumps to massage ones feet as well as soothing them and cooling them down).
- In some beauty products such as hair conditioners, based on natural ingredients.
- As an antispasmodic and smooth muscle relaxant in upper gastrointestinal endoscopy.
- In organic chemistry, menthol is used as a chiral auxiliary in asymmetric synthesis.