Menthol is a synthetically-made organic compound extracted from natural plants like corn mint, peppermint, and other mint oils. It is a waxy and crystalline substance that is either clear or white in color. Due to its local anesthetic and counter-irritant qualities, it is widely used for a variety of purposes like soothing minor throat irritations, such as in lip balms and cough medications or chest decongestants, and acting as a weak kappa opioid receptor agonist.
Menthol can also be commonly found in perfumes, aftershaves (to treat potential razor burns), oral hygiene products to reduce or treat bad breath like mouthwash and toothpaste (giving them their signature fresh and minty flavor), and most notoriously, as a smoking tobacco additive in most cigarette brands.
Menthol is added to smoking tobacco cigarettes to improve flavor and reduce throat or sinus irritations caused by smoking. Menthol is also added because it can increase nicotine receptor density in the brain, making smoking tobacco a much more addictive habit than it already is.