Mice fed large amounts of caffeine were calmed by smelling lavender and sandalwood.

Elderly British patients fell asleep more easily and stayed asleep after smelling lavender.

A New York hospital did a study which found patients undergoing MRI felt 63% less claustrophobic after smelling vanilla.

In a double blind study, women after pregnancy had less discomfort than the control group when lavender was applied topically.

ICU patients reported feeling better after receiving a topical lavender oil application than when they were given a massage or allowed simply to rest.

Mistakes made by Japanese keyboard operators were cut in half when the fragrance of lemon was pumped into their area.

Sixteen new mothers received aromatherapy massage two days after giving birth. Their post-partum depression was significantly less than the control group who received normal post-partum care.

A Japanese study suggested that “aromatherapy massage could be beneficial in disease states that require augmentation of CD8+ lymphocytes.” CD8+ lymphocytes “block HIV replication” so aromatherapy massage may have a real benefit for AIDS patients.

France treats aromatherapy more seriously, restricting the use of some essential oils to doctors and covering the cost of aromatherapy treatment through insurance. Apparently the French regard at least some aromatherapy applications as effective. In many countries (but not the United States, Russia, Germany or Japan), essential oils are included in the national pharmacopoeia, a book listing medicines and compounds which is issued under government authority.

Essentials oils are claimed to be 75-100 times more powerful than dried herbs.

The fragrances stimulate nerves in the nose, sending impulses to the brain. The roof of the nose collects 15% of the air we breathe. Olfactory receptors then pass the odors to the limbic region of the brain, an area “connected with instinct, mood and emotion.” Through this mechanism, aromatherapy is alleged to stimulate the release of chemicals in the brain which affect emotions. One article reports, unfortunately without citing details, that an EEG has traced a brain response four seconds after an essential oil was inhaled.

Richard Axel and Linda B. Buck published a paper in 1991 clarifying how we smell. They were awarded the Nobel Prize for Medicine in 2004 for this work. Olfactory receptor cells (OCR) are each keyed for only a few odors. There are about 1,000 different types of OCRs. The cells transmit nerves processes to glomeruli in the olfactory bulb; there are about 2,000 glomeruli. OCRs for the same odor share the same glomerulus. The olfactory bulb is the primary olfactory area of the brain. From the bulb, information goes to other parts of the brain via mitral cells, where input from several OCRs is used to form a pattern. This pattern equals an odor.

While smell is important to humans, particularly for survival (suggesting one may not want to eat rotten fish), it is even more important in other species. Dogs, for example, have an olfactory epithelium forty times larger than that in humans.

Humans can recognize and remember about 10,000 different smells. How these smells are gathered and interpreted is now understood. Whether the odors of essential oils have a cause and effect relationship (smell lavender, become calm) when they use this framework is less certain.

Applied externally, an essential oil’s effect is said to be partially through the odor and partially through rapid absorption through the skin. Purportedly, essential oils will “show up in the urinary system, [and] the lungs” soon after external application. One article reports that five minutes after essential oils were massaged into an arm for five minutes, a blood test “found the major chemical constituents from that essential oil in the blood of the arm.” Another source says it takes twenty to seventy minutes for the essential oil to be absorbed into the blood.

The bottom line is that while there is some evidence aromatherapy has an effect, the mechanism by which it does so is poorly understood. Most aromatherapy practitioners, it seems, feel that the oils do work and are relatively unconcerned about how or why the oils do so.

Although aromatherapy is not seriously regarded by science, there is circumstantial or anecdotal evidence that it works.

Our understanding of how aromatherapy works is speculative.