Eucalyptus incense has been widely used to relieve the symptoms of respiratory system congestion. Moreover, using an incense made of a mixture of peppermint and eucalyptus can thin the mucus, result in air duct dilation, and it can also help patients with chronic bronchitis and emphysema breathe more easily. Eucalyptus is an expectorant and Germany E Commission has approved its use for cough and bronchitis. The antiviral activity of the water soluble components of eucalyptus essential oil have been demonstrated in vitro.
Thymol and carvacrol have manifested a wide range of effectiveness against the bacteria involved in upper respiratory tract infections. The thymol and carvacrol present in thyme exert their antibacterial effects by forming a complex with bacterial membrane proteins. Furthermore, adequate doses of thymol and carvacrol have relaxant effects on the trachea. Commission E has approved the use of thyme for treatment of cough and bronchitis. Thyme relieves bronchial spasm and it is an expectorant with antibacterial and antiviral effects.
In Germany, doctors prescribe a pharmaceutical product containing common myrtle essential oil (Gelomytrol) as an expectorant and mucus dilutant (mucolytic) for patients with acute and chronic bronchitis and sinusitis. The expectorant properties of common myrtle have been substantiated in clinical trials conducted on patients with chronic obstructive airway diseases. Common myrtle essential oil contains alpha-pinene, limonene and cineole. Monoterpenes and sesquiterpenes present in common myrtle have antibacterial, antifungal and antiseptic effects. In animals in vivo, myrtle plant, Shirazi thyme and artemisia essential oils, with a dilution of 1.256, have entirely eradicated the avian and Newcastle flu.
In in vitro studies, menthol has an effect similar to that of surfactants. In in vivo studies menthol has reduced the surface tension in water-air interfaces which in turn results in improving pulmonary compliance (lung compliance). The results of the studies conducted on animals have manifested the effect of menthol as an antitussive in the treatment of coughs caused by chemicals. Based on experience, menthol helps patients breathe more easily during colds. The popularity and widespread use of products containing menthol such as topical nasal decongestants, lozenges, ointments and inhalers are indicative of this effective characteristic of menthol.