The Science of How Essential Oils Boost Mood

Neuroscientist and leading scent expert Rachel Herz, Ph.D., on the science of scent and emotion. Everything you need to know about how aromatherapy really works.

PhD Rachel Herz smelling a rose in Oxford, England.

Update: Rachel Herz will be speaking at SXSW 2021 in March.

By Molly Taft

Smells, memories, and emotions are all tightly bound together in our cultural conversation. One of the earliest mentions of smell and emotion in modern literature is in French author Marcel Proust’s In Remembrance of Things Past. Anyone who took an English class in college will undoubtedly remember the famous passage where the author is transported back to his childhood just by tasting a madeleine cookie dipped in tea.

But there’s more to it than traveling through time or the age-old history of aromatherapy.

There’s been an increase in clinical studies focused on aromatherapy in the past 30 years, and Rachel Herz, a neuroscientist at Brown University, was one of the first scientists to study the interaction between scent, psychology and biology. Her work separates the folklore of aromatherapy from the science of the effects of scent on human cognition, emotion and behavior.

“When I first started my PhD, no one was studying how scents could manipulate mood,” Herz said. “Then one paper came along which showed that smelling a pleasant odor put people in a good mood, and smelling an unpleasant put them in a bad mood. The authors speculated that it was due to the basic evolutionary meaning of scents and how scents are processed in the brain, and this set off a lightbulb in my brain!”

Herz became fascinated by the unique connection between the sense of smell, emotion and memory. She’s since become a leading expert on the psychological science of smell, authoring three books and more than 90 research articles on the topic. Some of her major academic contributions include showing how odor-evoked memory is emotionally unique, how “aromatherapy” really works, and how emotional associations to odors can change our moods and behavior.

“It became clear to me that regardless of other factors there is a psychological mechanism that underlies the brain’s response to scent,” she said.

And this mechanism includes aromatherapy and essential oils. Many people may think of aromatherapy as a purely holistic exercise with no scientific roots. But Herz’s work shows that scents used in the practice produce psychological reactions that are anything but imaginary.

“Aromatherapy is real. Mood, behavior and thoughts do change,” Herz explains. “But it works through the way our own mind and brain works.”

When a scent activates the brain, it can seem as though it has drug-like effects — but our psychology is really at the root of this reaction. There. are a couple of conditions that need to be present to see this effect: the smell needs to be at a detectable level, and we need to be at least slightly aware of it. When these two conditions are met, a response occurs — meaning that there are scientific and. psychological mechanisms at play in a true neuroscientific sense. At the inhalation of a smell, receptors in our nose are activated which sends signals to our brain. As soon as we consciously register the scent, specific emotions and moods are triggered.

Dr. Herz sat down with Mindalt to talk more about the science of smell, how our brains and our bodies respond to scent, and how to use essential oils to hack your moods.

Mindalt is a mood enhancing deodorant that harnesses the natural power of essential oils to boost mood.

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Q & A

Q. To start, can you tell us the difference between aromachology and aromatherapy?

In 1982 The Sense of Smell Institute came up with the term “aromachology” to refer to the legitimate study of smell and emotion. This term refers to the real psychological science of scent, not anecdotes from aromatherapy practitioners. They were establishing that there is a scientific basis to the effects that smells can have on our mood and behavior that can be empirically validated. But people tend to still call all of it aromatherapy. I now think of aromachology as real aromatherapy, not the folklore version of it.

Q. How does your scent research explain what happens in our brain when essential oils get inhaled?

A. Scents start by finding their way to the top of your nose, where scent molecules bind with millions of receptors. Those receptors send a signal into the brain and reach what’s called the olfactory bulb, a little projection at the bottom of the brain, level with your eyebrow. The bulb then sends that signal further into the brain to the limbic system, specifically the amygdala-hippocampal complex, which govern our emotions and memories.

The amygdala is where emotion and emotional memory are processed. The hippocampus is where associations are formed. Together, these two structures bind the smell and emotion and any memory or association we may have with that particular scent. This interaction happens almost immediately.

“Smells activate physiological and behavioral responses associated with emotions almost instantly.”

Unlike input we perceive through our other senses, input from our sense of smell bypasses other brain structures and goes directly to the limbic system where our basic emotional and motivational responses are processed. In doing so, smells activate the physiological and behavioral responses associated with these emotions almost instantly. This is why the smell of baking cookies can immediately make us feel happy and comforted and how smelling a bright citrus like lemon or bergamot can help us perk up and give us energy.

Q. What happens to our bodies when we smell certain scents?

A. It’s not just our moods — when scents trigger the limbic system, the brain initiates physical responses to those emotions. For example, a scent that your brain associates with invigoration — like peppermint or cedarwood — could cause your heart rate to increase.

From a neurological perspective, the instant response our bodies have to scent is pretty unique. In fact, the specific structures that make up the limbic system in our brain actually evolved from neural tissue that was originally dedicated just to processing of chemicals — that is, smells. This means that emotional memories and scent are fundamentally intertwined in our brain.

“We wouldn’t have the experience of emotion as we know it if we did not have a sense of smell.”

Something I like to say is that we wouldn’t have the experience of emotion as we know it if we did not have a sense of smell, because the amygdala and hippocampus evolved from being able to detect smells. Also, scents and emotions give us very similar types of information. Good smells tell us to go forward, to pursue what is in front of us; bad smells elicit disgust, or fear and withdrawal. Similarly, emotions help us survive — the good emotions make us go forth and multiply, while the bad emotions help us to get rid of or away from threats and protect us from demise.

Q. So what role does the nervous system play in the inhalation side of aromatherapy? In other words, how does what you call “real aromatherapy” work on our bodies?

A. The nervous system is the brain. The brain is the nervous system. As soon as your brain responds, your nervous system responds, with the immediate physiological response I talked about: I smell something, it makes me feel relaxed.

Let’s say I smelled something that I associated with my beloved grandmother, who may have recently passed away. I could get upset and start crying. All kinds of physiological things happen when I start crying. My heart rate, my skin conductance (perspiration), my hormone secretions — all these physiological transformations are happening, and it’s because of the emotion that was triggered by the scent. That’s what I mean by being real. A scent produces the same emotional and physiological impact as the event that it is connected to would.

A less intense example are the changes that take place physiologically with a scent that makes you feel relaxed. The scent has physiological downstream effects on the nervous system, and, as a result, on every system within your body. It affects your entire body, just like the emotion itself affects your entire body. Whether you’re feeling relaxed because you took an Ativan, or you’re feeling relaxed because you’re on a peaceful vacation, or you’re feeling relaxed because you’re smelling something that’s triggering soothing associations — the physiological responses are going to be very, very similar in all cases. The physiology part is real. The effect is real. It’s really happening in your body.

Q. One of the long-term effects of coronavirus that’s been in the news lately is how the disease can make some people lose their sense of smell. What’s that experience like?

Dr. Rachel Herz, pHd, neuroscientist at. Brown University

It can be devastating to lose one’s sense of smell. I once served as an expert witness for a young woman who lost her sense of smell in a car accident — it’s pretty common to lose your sense of smell with a head injury. When I met her, she’d recovered from all her physical injuries, except that she still couldn’t smell. Her smell loss was permanent and everything in her life had turned upside down because she couldn’t smell any more. Her relationship with her husband was falling apart. She decided she didn’t want to have children anymore. She couldn’t do the kind of work she did before. She had lost her sense of self. She had become paranoid. She became socially isolated. She had become very depressed.

This young woman told me she had never realized how her sense of smell was actually involved in almost every aspect of life.

Luckily, with Covid-19 most people regain their sense of smell within a few weeks of getting better, and there are methods for people with more long term loss to help them regain their sense of smell.

Q. Are essential oils different than other scents in terms of how they work on our body and brain?

Essential oils can get absorbed into your bloodstream via a topical application, depending on how much you use, and work with the nervous system to deliver an emotional response. But what’s most interesting to me about essential oils is the stability of the oil itself. First of all, having oil as a medium to deliver scents means that there’s going to be less change in terms of how it smells over a period of time — oils are much more stable than other mediums. The bottle you open up today, you open it up in a month, it should still smell the same.

Secondly, it’s going to be less volatile than other forms of scent delivery. For instance, fine fragrances are in alcohol, so the different aroma chemicals evaporate at different speeds. If you have something in oil, you have a much more consistent and constant smell.

Q. Does the level of essential oils in a formula or fragrance have an effect on its ability to trigger the emotional responses we are speaking about?

Intensity makes a big difference in terms of how we perceive any smell. It is also individual. Everyone actually has a unique nose, unless you have an identical twin. The olfactory sensory neurons that you have expressed in your nose are ever so slightly different from everybody else’s. Where this makes a real difference is in terms of how strong or weak things smell to you.

The stronger the smell the easier it is for us to detect it and recognize it, and the faster and more intense our emotional response will be. But there’s a caveat. If it smells too strong and we don’t like it because it’s so intense, our response could become negative. Having the right level of essential oil so that it is easily detectable and recognizable, but not overpowering, is key.

Q. How can we best appreciate — and use — our undervalued sense of smell and keep our own unique nose working?

I always advise that people should develop their own personal apothecary of special scents that make them feel a certain way or make them remember happy times. Or create new associations. Sniffing an essential oil when you’re feeling creative and getting work done can evoke feelings of productivity when you smell it later.

“Sniffing an essential oil when you’re feeling creative and getting work done can evoke feelings of productivity when you smell it later.”

I also advise rotating between a variety of smells so that you can keep your nose alert and maintain the original connections between the scent and a specific emotion. If you overuse a specific scent you’ll stop being able to detect it well, and it could eventually become associated to the experiences you’re having when you’re smelling it. So instead of making you feel focused and motivated it could make you feel bored and distracted.

You can even train your nose and your brain to make certain scents elicit certain moods. You can take a new smell and deliberately pair it with feeling really excited and energized or feeling really relaxed — whatever type of emotion you want to elicit. Then when you want to feel that way again, you go back to that scent. So when you’re first using a new scent, like with the blends in Mindalt deodorant, you can take that opportunity to establish an intention or a certain mood that your brain can then associate with that scent.

“I think that people should appreciate the smells around them — to take little moments throughout the day to breathe in scents and appreciate their effects.”

The morning is a great time for a small moment of mindfulness tied to scents. Breathing in a certain scent — like a deodorant — and setting an intention can help you find a grounding moment that allows you to enjoy a scent and its effects while preparing for your day.

Your nose is one of the most important tools you have to change your mood and alter your spirits. By finding moments to incorporate scents throughout your day, you can keep this superpower alive — and find new ways to stop and smell the roses.

To learn more the psychological science of scent see The Scent of Desire and rachelherz.com.

The Lark is where Mindalt, The mood enhancing deodorant. shares mood news and inspiration for making days and mornings matter.