The most powerful component in aromatherapy – and the one least understood or acknowledged – is the direct role our sense of smell has on our bodies. Why does ylang-ylang relax and rosemary stimulate? Why do some nail techs become immune to the smell of acrylic? It’s all about smell, memory, and the scientific magic that connects the two.
Think about a time you walked through a fragrant, flower-filled garden. Most people experience a sense of calm and well-being. The smell of the flowers stimulates the brain to have this pleasant reaction. Now think of a time when you smelled something awful, a rotten egg maybe. Your reaction was undoubtedly negative. The biological reasons for our reactions to bad odors are fairly clear to scientists – to protect us. However, the biological reason for pleasant odors is far less understood.
Our sense of smell is integral to how we perceive the world. Scientific studies have suggested that smell can influence mood, memory, emotions, mate choice, the immune system, and the endocrine system (hormones). The science of smell is fundamental to how aromatherapy works: the brain registers the Pure Essential Oil (PEO) molecule and delivers an immediate chemical response to the body via the nervous system.
Smell and taste are our two chemical senses. All other sensory experiences (touch, for instance) have much farther to travel the nervous system to the brain before being registered. Other senses are processed in more evolved and complicated parts of the brain that aren’t as instinctual as smell. That is why smell is so evocative, fundamental, and powerful. It is estimated that humans can distinguish up to 10,000 different smells.
In order for us to be able to smell (or sense) chemicals, they must have certain common characteristics. For instance, odor molecules must be small enough to evaporate and vaporize into the air so that they can reach the nose. The larger an odorant molecule, the less it smells. In aromatherapy, the high “notes” are the smallest molecules and evaporate the fastest. Thus, they are the first smells to reach our nose, but also the most fleeting. At the other end of the spectrum are the base notes, which are the heaviest and slowest to evaporate and reach our noses. So while they have less intensity, they are the longest lasting and most lingering odors.
Odor molecules must be water soluble to a certain extent in order to be absorbed into the nasal mucosa. After being dissolved and absorbed into the mucous, smells can then be detected in the nose by special receptor cells in the olfactory epithelium. Also found in the nasal mucosa is a pigmented type of epithelial cell. The darker the pigment, the greater the sensitivity to smell (i.e., lighter in humans and darker in dogs).
This pigment is thought to absorb infrared radiation and somehow play a part in our ability to smell. There are two olfactory bulbs, one in each nostril. There are about six million receptor cells in each human nostril (Animals who rely on their sense of smell to find food have more. Rats, for example, have 50 million.)
The limbic system is the region of the brain that deals with motivation, emotion, mood, instincts, and certain types of memory, as well as where certain vital functions for life are performed automatically. It was one of the first parts of the brain to develop from an evolutionary standpoint and controls some of our most basic instincts and functions. Humans and other primates have a direct pathway between the nose and the limbic section of the brain (because this part of the brain is closest to the nose) and then the olfactory cells to project to the thalamus and hypothalamus. This pathway is responsible for the effective component of smell. Smells can evoke colors in our mind’s eye. Memory is very often associated with smell, linked in ways not completely understood by science.
The word pheromone comes from the Greek roots of pherin, to transfer, and hormone, to excite. Pheromones are chemicals given off by animals of the same species to elicit instinctual responses (industrious fragrance marketers have put pheromones in products for people looking to attract members of the opposite sex). When you think of chemical attraction what is happening is an exchange of smells. The way our brains process the smell of one another’s pheromones accounts for that instantaneous bond that sometimes can happen. Love at first sight is probably really love at first smell.
It has been demonstrated that babies as young as one week old can tell the difference between their mother’s smell and a stranger’s. It is thought that breastfeeding mothers (of humans and animals) send some sort of signaling chemical (via smell) to start the suckling response in their newborns.
Psychological vs. Physiological
Is smell psychological or physiological? Both, actually. The two components work together and complement one another. In a recent study a group of subjects were given a dose of insulin once a day for four days while they were exposed to a particular smell. As expected, their blood glucose level fell in reaction to the insulin. On the fifth day they were not given the glucose, but only exposed to the odor and their blood glucose still fell significantly.
Recently, aromatherapy was analyzed using electroencephalography (EEG) in a study conducted by Dr. Tim Jacob, Professor of Bioscience at Cardiff University in the UK. EEG measures brainwaves and can be used to demonstrate some of the effects of smell. Relaxation increases in relation to alpha-wave activity in the brain. The more relaxed a person is, the higher her alpha brain wave activity, and the less relaxed the lower the alpha brain wave activity. Dr. Jacob knew that aromatherapists and herbalists consider rosemary a stimulant ylang-ylang a relaxer.
For his study, subjects were hooked up to EEG monitors and pre-relaxed to start an increase in alpha brain wave activity. This provided a baseline recording of EEG. Then either rosemary or ylang-ylang was applied to a facemask for them to breathe through and the EEG recorded again. There was a measurably difference in alpha brain wave activity (see graph). Rosemary did indeed excite and ylang-ylang relaxed the subjects.
Odorant conditioning happens when neural activity changes its pattern in response to the same odor over time, depending upon the previous stimuli. Olfactory fatigue, which might be thought of as a type of odorant conditioning, is of special interest to nail technicians as it explains why nail techs can become “immune” to the smell of their acrylic liquid. The chemical molecules are still entering the nose and being absorbed and registered, but neural patterns are changed in response to long-term exposure. Although not always, foul odors are meant to be a deterrent (although there are very deadly chemicals – carbon monoxide, for example) that have no smell at all. When we ignore our own body’s signals and continue to expose ourselves anyway, we are conditioning our brain falsely to think that the odor is not bad. Overexposure can result when the olfactory fatigue level is reached.
If you’ve dabbled in aromatherapy before, then you know that some specific pure essential oils are contraindicated in certain circumstances, among them epilepsy pregnancy, young children, and high blood pressure.
As an example, with epilepsy, an epileptic moment (which is a faulty brain wave firing) can become a seizure depending on the level of arousal (brain wave activity) in the part of the brain surrounding the faulty discharging neurons. Seizures are less likely to occur when brain wave activity is at an optimal level. This level can be altered by many things, some controllable, some not. Smells cause activity in the same brain areas where epilepsy often starts. For this reason, aromatherapy is not recommended for epileptics. But when administered by a trained physician, aromas can be used to help epileptics.
When the sense of smell is lost or diminished greatly, the condition is called anosmia. It can be brought about by head trauma or sometimes a cold or virus. It has also been observed as a side effect of Alzheimer’s disease. Many people with anosmia become depressed, hinting at how great an influence or sense of smell impacts our quality of life.
Surely one of the earliest forms of aromatherapy stems back to primitive times when the “smoking of the sick” was performed by burning different woods and plants for medicinal purposes. Modern scientific knowledge verifies that there were very good reasons for choosing specific woods for specific types of illnesses; many of the woods traditionally used (lavender, cypress, cedar) are known to have antiviral, antibacterial, and antiseptic properties. Recent uses of aromatherapy for healing the sick include a research project at Gunderson Hospital in LaCrosse, Wis. Heated, flax-seed-filled pillows with lavender are being used with success in treating cardiac patients postoperatively for pain and depression, according to Karen Kowal, R.N and founder of MotherEarthPillows.com, who is supplying the aromatherapy pillows for the study.
The route for a smell from nose to brain may seem short. But there is a lot going on from when we take a whiff to the powerful biological and chemical reactions that then take place.
Chemical Composition of Pure Essential Oil
So where do Pure Essential Oils (PEOs) come from? They are an extract of plants and roots and are considered the inner core of the plant’s life force. Just as our DNA is what makes us each unique and different. PEO is like the DNA of a plant. It is what makes each plant unique from another of the same type. Some would even say the PEO is the “soul” of the plant, like its hormones or its essence (hence the term essential). Some PEOs are smaller than a human skin cell, facilitating absorption from the dermis (top layer) to the epidermis. Another characteristics is the PEOs are lilophilic, which means that they are attracted to fat cells. Since our skin has a subcutaneous layer of fat cells, the absorption rate is enhanced. Since the dermis contains many capillaries, the PEO can pass from the dermis into the bloodstream. However, PEOs do not seem to remain in the body as long as traditional chemical drugs and are expelled in many ways often in as little as three to six hours’ time.
Climate and location have a great effect in a PEO’s effectiveness, so quality can vary depending on the locality where the plant was grown. The method (distillation, extraction, expression, solvents) by which the PEO is extracted also plays a role in the quality of the final product..--Barb Wetzel