What Happens When We Smell Essential Oils?

One of the most well-known impacts of essential oils on the body is the emotional impact. This is a phenomenon that occurs because of our sense of smell, or olfaction. But what actually happens when we smell essential oils? Two key things that involve the whole brain: olfactory signaling and absorption.

Sense of Smell & Essential Oils

Olfactory signaling is a primitive response in the body connected to ancient parts of our brain. It involves first detecting an odor and then an emotional response that follows. When we inhale an odour molecule, it lands on tiny hairs in the nose called cilia. These cilia vibrate and create an electrical signal, which travels to a receptor cell. These cells are capable of detecting thousands of different odors. The receptor cells send the information to the olfactory bulb, which has receptors that are part of the brain and further sends messages to the primitive parts of the brain. Here they influence emotions and memories.

So essentially, the odor is detected and the brain is signaled from the smell. The process is fast, and it’s partly a survival mechanism, but also tied to homeostasis. We use it mostly for food purposes, but we also use it to identify threats. As basic as things like identifying sour milk or rotten food, garbage for example. Unsanitary conditions. We all know what happens when we smell these odors. Our bodies physiologically reject it, sending us signals of disgust. Sometimes making us vomit or gag.

But it exists to teach our bodies not to ingest something or to seek out food. As metabolic energy reserves decrease and hunger develops, then food smells, specifically, also become more appetizing. This promotes food-seeking and consumption. So it teaches us to go find something to eat. A reason why food smells especially good when you’re hungry. That is part of governing homeostasis in the body.

Smell also signals us on things like reproduction. We know some people smell so gross and we do not want to date them or have sex with them and we are not attracted. Science isn’t really sure if it’s because we attach emotional response to smell or if it’s a biological response. There’s a lot of myth and hype and marketing around this idea for things like colognes and perfumes etc. We don’t know really well how it works yet, and some ideas might be junk ideas, but we do know that we have this response.

Some of the things mentioned may also classify as emotional response and physiological response. But let’s talk about this emotional thing. People often have a hard time understanding how it’s possible to do emotional healing with aromatherapy, but there is a clear emotional shift or response that happens in the limbic brain in response to smell. When we smell an essential oil.

We have the age-old example of smelling fresh-baked bread reminding us of grandma’s house and the happy and safe times we had there. But we also know that people who live with PTSD, can also be affected by smell.

Smell, and olfaction, is a known trigger for flashbacks. Smell serves as a cue for memory formation and emotional conditioning. We don’t fully understand why smell evokes this emotional response exactly, but we do know that it is closely linked to the emotional or limbic brain. This is a part of the brain that actually does a lot of things. It involves:

  • Hippocampus — forming short- and long-term memories.
  • Amygdala — emotions like anger, sadness, fear; stores memories; involved in sexual activity and libido.
  • Hypothalamus — controls homeostasis, sleep patterns, releasing hormones, regulating emotional response
  • Thalamus — sends sensory information to the cerebral cortex

So this part of the brain is responsible for emotions but also looks after all these other mechanisms and functions in the body.

The second piece of essential oils in the brain is absorption. This is the effect that essential oils have on neurons and the effect on neurochemicals. Essential oils are made of small molecules. As these molecules are inhaled, they are able to pass through the blood-brain barrier and affect the brain. This is important for brain diseases where certain drugs are not able to cross the barrier. Things like Parkinson’s and Alzheimer’s and epilepsy, for example. But it’s also important for things like cognition, alertness, memory, focus, concentration, learning, and mood.

We don’t fully know how these essential oils work in the brain. There are many things to consider when you’re talking about action in the brain: does it block synthesis of a naturally occurring chemical, does it block movement down an axon? Or block release into the synapse? Or block attachment to a receptor? When we look at drugs, it’s not even fully understood exactly which mechanism is at play so we can’t assume we know how oils work.

But we do know some things. We know that some constituents affect enzymes. Things like fenchone and carvacrol inhibit acetylcholinesterase, which is an enzyme that catalyses the breakdown of acetylcholine. Drugs that inhibit acetylcholinesterase, and butylcholinesterase, another enzyme, are used to treat Alzheimer’s disease. In AD, it seems the balance or ratio between enzymes is important and changes in different stages of the disease. It appears that inhibiting those enzymes might be beneficial to the disease and symptoms of the disease.

We’ve been talking about essential oils’ ability to inhibit these enzymes since at least the 90s, but some preliminary research was actually published on this effect on Alzheimer’s disease in 2015. That research article is in the show notes if you want to check it out, but it basically says that certain essential oils had dose-dependent effects on these enzymes.

We also know that essential oils can stimulate the release of dopamine and serotonin, which are well-known chemicals involved in regulating mood. We know that essential oils can reduce anxiety and depression and improve sleep patterns.

Some constituents and essential oils also influence the GABA system, GABA receptors, GABA enzymes, acetylcholine receptors, and NMDA receptors. Generally, disruption in these systems leads to disruption in electrical signaling, which can lead to seizures. The reason why this happens can be caused by things like damage to the brain, or a head injury for example. When we look at certain essential oils, they can negatively affect these systems, which can cause seizures. Oils like hyssop, sage and others for example.

But other oils can actually positively affect the systems and reduce seizures.

The process of how essential oils work in the brain through inhalation is complex, and we don’t fully understand it. We do know that oil molecules are small enough to cross the blood brain barrier and enter the brain, and we also know they do interact with enzymes, receptors, stimulate the brain to release brain chemicals, and interact with the central nervous system and specific parts of the brain.

This may have great benefits for people who live with neurological conditions and managing symptoms. Does it mean it’s a treatment? No. We’re not there. But it could be a complementary therapy within those conditions to improve symptoms.


So what are some of the precautions we need to discuss?

Going back to epilepsy, the natural question that follows this discussion is: if inhaling an essential oil affects the brain, can inhaling one of those epilepsy-risk oils cause a seizure? The answer is, for sure it can, but it’s rare. The seizure-inducement generally comes from higher doses and generally from ingestion.

The oils do not statically cause a seizure. Meaning, a seizure doesn’t occur in every person who uses those essential oils. Hyssop will not cause a seizure in every person who uses it. So maybe what’s most important here is that if a person is taking anti-seizures medications, certain oils may interact with those medications, causing them to be less effective, and influence the system, which then can lead to a seizure. It’s possible that smelling it can interact with that medication, and the system, but in most reports, the seizures occur as a result of ingestion.

Smell can be a seizure trigger for some people, so if you’re one of those people, then use extra caution. Generally, if you have epilepsy, you’re going to make sure to avoid those risk oils, and focus on the ones that have a positive effect. For anyone concerned about this, check out this essential oil safety guide.

Headaches are possible. Often this happens with poor quality essential oils. If you’re using fragrance oils or body shop oils, this is not an essential oil. It’s a perfume and no better than one of those tree air fresheners in the car. It will give you a headache. You’re literally inhaling fumes into your brain. I cannot stress quality to you enough.

But authentic essential oils are not exempt from this. New aromas or strong, intense diffusion in a closed space with a strong-aroma essential oil may give you a headache. There are times when deep inhalation of authentic oils can be effective. Like deeply inhaling peppermint during mood disorders, or lavender during high stress. Or eucalyptus for alertness. I usually do this with a diffuser but also from my palms and or a blending bowl.

But sometimes doing that for too long isn’t helpful. So pay attention to how you feel and turn it off when it’s enough.

Strong emotional release is also possible when we smell essential oils because it is stimulating those brain centers. Emotional response to smell is very personal and flexible. Some people do not have strong reactions. Sometimes nothing major occurs, but some people burst into tears and have a real moment and often do not understand why or what’s happening. In those moments, I like to encourage people not to avoid the moment or to turn off the tears but to follow it wherever it goes. Sometimes we’ve just been holding in emotional pain and we need to let it go and release some sadness and emotion in order to heal.

Sometimes people have negative emotional responses to certain oils based on perhaps a certain smell being connected to something unpleasant. In those cases, I would suggest avoiding those smells and do some emotional work in an appropriate manner. You might lean towards some more soothing aromas instead.

Sometimes people experience calmness, especially if they’ve been anxious or agitated. This works well with aggressive behaviour in children and adults, or neuro-atypical individuals, and PTSD sufferers. In some of my work, I’ve worked with some individuals with PTSD who didn’t find much effect through applying essential oils to the body, but simply diffusing them took away what they described as skin crawling and edginess that made the triggers so much worse.

Treatments or Complementary Therapies?

So are these treatments? No. We’re not there. But they can be complementary therapies and assists with other programs that help manage symptoms.

So really, the effect of essential oils on the brain is pretty complex. I believe there’s a lot of potential here in aromatherapy for therapy settings and for people suffering with mental health disorders and neurological diseases as complementary programs. One of my dreams is to see gentle aromatherapy being used as assists in places like schools and daycare settings and therapy settings and long term care homes. Even prisons and psych hospitals. If we could relieve some anguish by smelling an authentic plant oil that has very little to no negative side effects, what positive impact could come from that?


Cheryl Whitten is a Clinical Aromatherapist. She writes about aromatherapy and natural wellness at livelovelemon.com.

Clinical Aromatherapist. Writer. Podcast Host. Helping women and families find wellness. Naturally.