Contrary to popular opinion, there actually is some research showing the effectiveness of many EOs as well as how or why they work. The smell receptors in our noses are the only sensory input organ that sends signals directly into the brain rather than filtering them first, and this is thought to be at least part of why they work. Essential Oils can be very problematic for people with mast cell disease or other allergic diseases (probably eosinophilic diseases as well), so if you have or suspect you have MCAS please be careful. Because EOs tend to be very high in salicylates people who do not tolerate them should probably also be cautious. The following is research that may help us to choose the appropriate oils.
What are the benefits of aromatherapy?
"Essential oils used in aromatherapy are typically extracted from various parts of plants and then distilled. The highly concentrated oils may be inhaled directly or indirectly or applied to the skin through massage, lotions or bath salts. Aromatherapy is thought to work by stimulating smell receptors in the nose, which then send messages through the nervous system to the limbic system — the part of the brain that controls emotions."
Adverse effects of aromatherapy: a systematic review of case reports and case series
3 Reasons to Avoid Ingesting Essential Oils
Why essential oils are not water flavoring agents
Some EOs have been shown to cause or worsen seizures in some people, and should be avoided by people at risk for seizures. This post lists out which oils these are, and explains why they can be problematic. If you scroll to the bottom of the post, it also has information about which EOs might help with seizures.
ANTIMICROBIAL EFFECTS (emphasis added in quotes below)
Essential oils from aromatic herbs as antimicrobial agents.
"Bacterial resistance to multiple antibiotics is a health problem. Essential oils (EOs) possess antibacterial properties and have been screened as potential sources of novel antimicrobial compounds. Terpenes and terpenoids are components derived from EOs. Some of these EOs show inhibitory activity against Staphylococcus aureus. Carvacrol has specific effects on S. aureus and Staphylococcus epidermidis. Perilla oil suppresses expression of α-toxin, Staphylococcus enterotoxin A and B and toxic shock syndrome toxin. Geraniol shows good activity in modulating drug resistance in several gram-negative species. EOs could act as biopreservatives, reducing or eliminating pathogenic bacteria and increasing the overall quality of animal and vegetable food products. Although clinical studies are scarce, the uses of EOs for topical administration and as penetration enhancers for antiseptics are promising. Little information exists for oral administration."
Antibacterial and antifungal properties of essential oils.
Some Essential Oils Inhibit MRSA, Influenza, and Strep - Scientific Studies
This is a very helpful post on another person's blog that includes a long list of studies and summaries of what the research found.
Vapor-phase activities of cinnamon, thyme, and oregano essential oils and key constituents against foodborne microorganisms.
"The aim of the study presented here was to gain knowledge about the vapor-phase antimicrobial activity of selected essential oils and their major putatively active constituents against a range of foodborne bacterial and fungal strains. In a first step, the vapor-phase antimicrobial activities of three commercially available essential oils (EOs)-cinnamon (Cinnamomum zeylanicum), thyme (Thymus vulgaris), and oregano (Origanum vulgare)-were evaluated against a wide range of microorganisms, including Gram-negative bacteria (Escherichia coli, Yersinia enterocolitica, Pseudomonas aeruginosa, and Salmonella choleraesuis), Gram-positive bacteria (Listeria monocytogenes, Staphylococcus aureus, Bacillus cereus, and Enterococcus faecalis), molds (Penicillium islandicum and Aspergillus flavus), and a yeast (Candida albicans)". The results of the study are complex and hard to summarize so please follow the link for more information.
Antifungal activities of essential oils and their constituents from indigenous cinnamon (Cinnamomum osmophloeum) leaves against wood decay fungi.
Effects of oregano, carvacrol and thymol on Staphylococcus aureus and Staphylococcus epidermidis biofilms.
Biological and Pharmacological Activities of Carvacrol and Carvacrol Bearing Essential Oils
Smelling lavender and rosemary increases free radical scavenging activity and decreases cortisol level in saliva.
Effect of lavender aroma on salivary endocrinological stress markers.
"These findings suggest that lavender aroma has a stress relief effect."
Protective effects of lemongrass essential oil against benzo(a)pyrene-induced oxidative stress and DNA damage in human embryonic lung fibroblast cells.