Inhaled peppermint, rosemary and eucalyptus essential oils do not change spirometry in healthy individuals

Essential oils of herbal origin are widely used in the treatment of diseases of the upper and lower respiratory tract primarily due to their antibacterial and antiviral effects. Menthol, the major component of the essential oil of mint (Mentha) species, exhibits antispasmodic activity, which might result in improved lung function. In a randomized experiment, 106 healthy participants received nebulized peppermint, eucalyptus, or rosemary essential oil for 15 min or no treatment (control). None of the essential oils had an impact on the measured spirometric variables (forced vital capacity, peak expiratory flow, the ratio of the volume of air forcibly blown out in the first second to forced vital capacity). Participants' expectations regarding the effects of essential oils did not affect their objective performance, however, they predicted perceived (subjective) changes. Perceived and measured changes were not connected with each other. In conclusion, inhaled rosemary, peppermint, and eucalyptus essential oils' subjective (perceived) effect on spirometry is mediated at least partly by expectations.