What Science Says About the Potential Healing Effects of Essential Oils

This article was originally published on Feb. 18, 2020.

Since the dawn of civilization, people have turned to the power of plants for healing purposes. But one folk medicine in particular seems more popular than ever: essential oils.

Today, there’s renewed interest in using essential oils to improve physical or psychological well-being. One poll found that a third of Americans believe in the health benefits of essential oils and aromatherapy. No longer niche, these little vials of plant essence are a billion-dollar industry, favored by Gwyneth Paltrow and grandmas alike.

With around 90 essential oils on the market — each with its own purported healing qualities — there’s a so-called “cure” for practically everything. Lavender, sandalwood and bergamot are popular essential oils for stress relief. Varieties like ylang-ylang and jasmine are reputed to boost libido. Some, like lemon oil, are believed to address a laundry list of conditions: morning sickness, pain and acne, to name a few. But there’s a problem with essential oil claims: Science hasn’t caught up to their popularity. There simply haven't been enough large-scale, peer-reviewed studies in humans to prove whether essential oils really can improve health or mood, or support any other commonly bragged about health benefits of essential oils.

With this in mind, let’s clear up what essential oils are, how they are thought to work, and what research says about them.

Essential oils are highly concentrated extracts of plant material — such as seeds, flowers, stems or roots.

But it can often be tough for consumers to know what they’re really buying. The market isn’t regulated, so there tends to be a lot of variation between essential oils — even among those that originate from the same brand.

“The constituent makeup of essential oils will vary from batch to batch, as they are drawn from plants that vary from country to country, field to field and even within the same plant from morning to evening,” says Mark Moss, a psychologist who studies essential oils at Northumbria University in the U.K., in an email to Discover. “The major components will always be there, but the relative concentration will vary.”

Another important thing to keep in mind is that essential oils haven’t been put through rigorous FDA testing and approval like the over-the-counter drugs available at your neighborhood pharmacy. So what essential oils do for health, if anything, is still pretty murky.

“Essential oils are neither medicines nor drugs because the effects have not been fully assessed yet in terms of science,” says Hideki Kashiwadani, a physiology researcher at Kagoshima University in Japan, in an email to Discover. 

Despite this, essential oils have wide appeal, particularly among people who have grown dissatisfied with modern Western medicine. And this alternative therapy is showing no signs of slowing down.

Most essential oils are inhaled via diffusion or applied topically to the skin after being mixed with a carrier oil. Other essential oils are supposed to be ingested, but medical professionals and health authorities generally warn against the safety of this method. 

When essential oils are inhaled via aromatherapy, compounds are absorbed through receptors in our noses, which send messages to our olfactory system, the part of the brain responsible for our sense of smell. Eventually, these messages reach other areas of the brain, such as the limbic system, which plays a role in our emotions. 

Read more: The Sense of Smell in Humans is More Powerful Than We Think

When essential oils are applied topically for cosmetic reasons or to treat aches and pains, the compounds are absorbed into the skin and eventually enter the bloodstream before they’re metabolized by the liver. 

But beyond that, even scientists have a tough time figuring out what various essential oils really do. Since there are no accepted standards for essential oils, Kashiwadani explains that scientists often find it challenging to replicate another scientist’s experiment.   

“One of the problems with essential oils and the lack of standardization is that you can’t tell if two researchers are actually testing the same essential oil,” Moss says.

But other issues — which are surprisingly commonplace in scientific research — further complicate matters. For instance, human studies on essential oils are few and far between. Of the research that has been conducted on humans, many studies involved small numbers of participants, which can skew results. As a rule of thumb, reviews or meta-reviews, which draw conclusions from large numbers of similar studies, tend to be the most reliable and comprehensive.

We also must remember that correlation does not equal causation. In other words, a mere association between two things isn't enough to prove a direct cause-and-effect relationship. So, even if a study found people who smelled lavender aroma felt less anxious, something else may be responsible for the effect (such as controlled breathing).

On top of that, the results from scientific studies can sometime be misinterpreted or blown out of proportion. When scientists study treatments, they’re looking for changes that are "statistically significant." All this means is that the results cannot be explained by random chance alone. So the impact of an essential oil might be scientifically significant, but fall far short of what we might view as meaningful.

In light of the shortcomings of essential oil studies, a lot of the information concerning the health benefits of essential oils tends to be anecdotal or rooted in folklore. And their safety hasn’t been fully vetted. So it’s important for people to remember that natural or organic doesn’t directly translate to being “safe” or “beneficial.” Plant compounds — especially in high doses — can be toxic, irritating or may cause allergic reactions or drug interactions.

But essential oils may not be totally worthless. Based on his own work, Moss said rosemary, sage and peppermint oils might improve memory and cognition to a degree. He also says lavender has been linked with improved sleep. Just don't expect essential oils to be magical elixirs. They're a far cry from being medication, and shouldn't replace standard medical care.

“The effects of essential oils are small. They are not a panacea. They can provide small benefits for individuals and should, in my opinion, be seen as self-care life enhancers rather than treatments as such,” Moss said.

If anything, many essential oils smell nice. So, if spritzing your pillow with lavender oil brings enjoyment and relaxation — even via the placebo effect — is there really anything wrong with that?  

“Don’t go searching for solutions to problems. Consider the potential for enjoying the experience. That is a benefit in itself,” Moss said.

Read more: The Power of the Placebo

Are essential oils safe and effective treatments for certain medical conditions? The jury's still out, but Discover rounded up some of the published work that explores the effects of some popular essential oils in animals and humans. If you’re thinking about trying essential oils, make sure you check with your doctor first.

The woodsy aroma of rosemary may do more than perk up a roast chicken. A small study of 20 people from Moss’ research team at Northumbria University linked rosemary to improved memory and cognition, particularly among older adults.

Another small study from Moss' team found that rosemary might improve test scores among school-aged kids. Children who took tests in rooms scented with rosemary received higher scores than children in nonscented rooms.

Despite his work investigating rosemary, Moss said he's not necessarily an advocate of promoting the use of essential oils, but thinks consumers should be able to make their own choices.

Lavender is one of the most popular scents in aromatherapy. Studies in both mice and horses have found that the scent of lavender is calming. In humans, small-scale studies found that it might have a modest effect on anxiety.

One study of 100 people found that lavender slightly improved anxiety before surgery. The researchers cautioned, however, that additional research is needed before drawing conclusions between lavender aroma and anxiety.

Taking lavender oil capsules orally might also have some effect on anxiety. That's according to a meta-analysis of five studies that involved more than 500 people, which looked at how lavender capsules measured up to a placebo and some anti-anxiety drugs. Although lavender capsules (also known as silexan) helped with anxiety, it also caused unpleasant side effects like nausea, belching and diarrhea in some people.

Lavender is also a common sleep aid. A review of studies concluded that it may offer some small to moderate sleep-promoting benefits. However, the review called for larger and more rigorous studies that investigate lavender and sleep.

Beyond that, lavender may have some pro-social benefits. A study that involved 90 people found that the aroma of lavender was more effective than a control in promoting a sense of trust among strangers.

But lavender oil maybe isn’t a good idea for everyone. It may be a hormone disrupter, and studies have linked regular exposure to lavender oil with abnormal breast growth in girls. Lavender (and tea tree oil) was also found to cause abnormal breast tissue growth in boys.  

Peppermint oil, which may have pain-relieving qualities, has been used for centuries to treat gastrointestinal problems. But unlike some other essential oils, there's pretty sound evidence to back up these claims. Reviews of studies have found that taking peppermint oil capsules may ease irritable bowel syndrome symptoms, like gastrointestinal pain.

A small pilot study also found that peppermint oil capsules may be helpful for people who have problems swallowing during meals or experience noncardiac chest pains. Consuming peppermint tablets helped ease discomfort in these patients, likely because the compounds helped to relax smooth muscles in the lower esophagus.

Tea tree oil is often found in cosmetic products because of its purported anti-microbial and anti-inflammatory properties. When applied to the skin, tea tree oil might be an effective treatment for mild to moderate acne.

A review study found tea tree oil was better than placebos, and just as effective as benzoyl peroxide, in stopping pimples. In addition to acne, several older studies suggest tea tree oil may be helpful for nail fungus and athlete’s foot.