All essential oils have some antibacterial — antimicrobial effect, so oils may be chosen for other reasons and still be effective. Also, as more and more infectious conditions become resistant to various antibiotics, the essential oils seem to retain there effectiveness. Essential oils produced by plants have been traditionally used for respiratory tract infections, and are used nowadays as ethical medicines for colds. In the medicinal field, inhalation therapy of essential oils has been used to treat acute and chronic bronchitis and acute sinusitis. Inhalation of vapours of essential oils augmented the output of respiratory tract fluid, maintained the ventilation and drainage of the sinuses, had an anti—inflammatory effect on the trachea and reduced asthma. Use of tea tree oil itself, did not become common practice until researcher Arthur Penfold published the first reports of its antimicrobial activity in a series of papers in the 1920s and 1930s. In evaluating the antimicrobial activity of M. alternifolia, tea tree oil was rated as eleven times more active than conventional phenols!
