Bacteria are one-celled organisms that cannot be seen without a microscope, living just about everywhere inside and outside the human body. Many bacteria are good for us, including those that live in the digestive tract and break down the foods we eat into nutrients and waste. Others cause diseases, illnesses, and infections. Tuberculosis, strep throat, staph infections, urinary tract infection, cholera, pneumonia, diphtheria, botulism, typhoid, meningitis, tetanus, Lyme disease, and many venereal diseases are all caused by bacteria.
Purveyors of essential oils have long claimed that many of these oils have the ability to guard against harmful bacteria. Until very recently, no scientific evidence existed to suggest that these claims might contain a kernel of truth. Thanks to the interest of the food packaging industry, however, a number of studies now point to the potential of essential oils as antibacterial agents, perhaps making them valuable in preventing bacteria from developing in packaged meats and other perishable products.
A study published in Microbios (Pattnaik et al., 1996) found that eucalyptus, lemongrass, orange, and peppermint oils were effective against 22 bacterial strains, while aegle (Indian bael) and palmarosa oils inhibited 21 different kinds of bacteria. The following year, Pattnaik broke down the oils into their constituents to determine what characteristic of the oils had the greatest effect on bacteria. He discovered that linalool, one of the aromatics in the oils, inhibited 17 of the 18 bacteria on which it was tested, while cineole and geraniol prevented the growth of 16 of the bacteria.
A 2016 study by Radaelli et al. published in the Brazilian Journal of Microbiology examined the antibacterial activity of six essential oils commonly used as condiments in Brazilian cooking. The results indicated that rosemary, basil, marjoram, thyme, and peppermint essential oils all had the ability to kill bacteria in a laboratory, while anise, the sixth oil tested, did not. “The use of essential oils from these common spices might serve as an alternative to the use of chemical preservatives in the control and inactivation of pathogens in commercially produced food systems,” the paper concluded.
More recently, in 2017, Puskárová et al. tested six essential oils—arborvitae, clary sage, clove, lavender, oregano, and thyme—to determine their antibacterial properties against a range of bacteria including E. coli, salmonella, staphylococcus, listeria, and others. The team found that oregano, thyme, clove, and arborvitae performed well against all the bacteria tested, even when the oils were used in reduced concentrations rather than at full strength. The study experimented with two application methods: researchers applied the oils directly to the bacteria in a laboratory and also infused them as vapor. The vapor trail determined that the oils inhibited the bacteria as well as the direct-application method did, apparently indicating that they could be used to kill bacteria in an open environment, such as disinfecting the air in a room.
A study published in October 2020 in the journal Antibiotics tested 15 essential oils in a laboratory setting against strains of E. coli and S. aureus (MRSA) that are proving to be resistant to traditional antibiotic pharmaceuticals. The researchers broke the oils down into their constituents and tested each of them individually against the targeted bacteria. They found that compounds called thymol and carvacrol, found in Lippia origanoides essential oil—an oil already in use as a food preservative—showed the most antibacterial activity of all the substances tested. They cautioned, however, that this oil has the potential to be toxic in the human body, so it would not necessarily be a viable alternative for patients with MRSA or E. coli to take internally.
These are just a few of the studies that indicate that some essential oils have the ability to fight harmful bacteria. A review of all the research on essential oils through 2016, published in the journal Evidence-Based Complementary Alternative Medicine (Swarmy et al., 2016), noted that three plants in the Achillea (yarrow) family have shown an ability to counteract certain pneumonia bacteria, as well as S. aureus, E. coli, and strep and staph germs. Six varieties of Artemisia (daisy) appear to have bacteria-fighting components, as do specific species of ajwain, anise, basil, bay laurel, bitter melon, black pepper, cinnamon, citronella, clove, coriander, cumin, cypress, fennel, kumquat, lavandin, juniper, menthol, melaleuca (tea tree), myrtle, oregano, parsley, patchouli, rosemary, summer savory, Salvia mints, thyme, verbena, and Warionia, a Saharan plant. This long list of plants and their constituents have been the focus of much scientific research worldwide over the past 20 years.
All the research has taken place in laboratories using isolated compounds and bacteria in agar or Petrie dishes, however, and only a few studies have reached phase II, in which the substances are tested using laboratory mice. To date, no studies have produced recommendations for use of these oils to defeat infections in the human body—which means that there are no guidelines to suggest how much of the oil would be required to treat a person, how it should be administered, and if there could be side effects from the oil’s potential toxicity.
A day may come when essential oils can be used to cure human illness, but that day is not here yet. Much more research will be required to translate the early findings of these studies into practical use to benefit actual patients.
