Menthol is a terpene with a strong minty and cooling odor. It can be produced from peppermint oil or artificially derived from the hydrogenation of thymol. 

Menthol acts as an anti-irritant by initially stimulating nociceptors and then desensitizing them, while providing a cooling effect. Menthol selectively activates the transient receptor potential melastatin-8 (TRPM8) channels and helps to modulate the contraction and relaxation of blood vessels. 

Menthol, when inhaled, can reduce airway pain and smoke irritation along the airways. Menthol also helps to suppress coughing and provide the sensation of easier breathing.