"Throw away the crutch of knowledge and use the Knowing..." Thomas Elpel.

The Power of Plant Oils is a forum for learning about the therapeutic use of essential oils.
This 13 module course is a means of acquiring the knowledge and experience so you can KNOW the properties
and uses of the plants and their oils.

Please read this blog from the bottom up and check out previous posts to the right under Blog Archives.

Sunday, March 13, 2016

Sedona Essential Oil Adventure April 16th-20th. Join us!

Calling all essential oil enthusiasts! Here is an opportunity to learn about our native Southwestern essential oils from two experts: Clare an Max Licher of Sedona Arizona. Register before April 1st to receive the special workshop price of $680.00 (contact Dr. Moore for details at 530-613-0831.)

SEDONA, ARIZONA  April 16-20th 2016 - Sign up soon!

Experience first-hand the joy of collecting plants for distillation at a small, boutique distillery in Sedona, Arizona. Clare and Max Licher, our hosts, are extremely knowledgeable about the Southwestern plants and their traditional usages.

I believe that American Aromatherapy should involve a greater understanding of our native plants and the healing properties they have to share with us. This journey offers a personal experience with these gifts. Our adventure includes an appreciation of the beautiful red rocks of Sedona as well as the history of the surrounding region.

An expert on plant taxonomy with an amazing, heart-centered connection to the local flora and fauna, Max will take us on a plant walk at Oak Creek Canyon outside Sedona where he will teach us about the properties and habitats of the native plants. Working in conjunction with local universities, Max has discovered several new species. Clare and Max both cultivate a deep reverence for the healing gifts that these plants have to offer us.

We will have the opportunity to bring back our treasures to the Licher's studio, to load the retort, and to watch the amazing alchemy as the raw plant material transforms into "liquid gold".

Antelope Canyon
This  trip includes an over-night sortie to Antelope Canyon and Vermillion Cliffs. At Antelope Canyon, we will have a private, guided tour of the stunning rock formations. We will stay at the historic Cliff Dwellers Lodge at Vermillion Cliffs where we will also have an opportunity to learn about and collect the regional aromatic plants.

Costs include the workshop, day excursions, private guided tour of Antelope Canyon, ground transportation and the priceless and unique educational treasures that this experiential trip provides.

Most meals, lodging, and airfare to Phoenix are not included in the costs.

Trip insurance is encouraged. (Try World Nomads at www.worldnomads.com or Travel Guard.)

To register or for more information, please contact Dr. Moore at 530-613-0831.

Saturday, March 14, 2015

Airlines Using Scents for Branding

Someone needs to clue in the airlines about the dangers of artificial fragrances:

What’s That Smell?

by Daniel Nikulin, travel bogger at www.flightcenter.ca

February 5th 2015
With so many outside factors around to disrupt our travel experience, airlines have been taking a closer look at areas they can control to help relax their passengers. After plying us with liquor and soft music  in their pre-departure lounges, comforting us with amenity kits complete with blankets and sleep masks when we board, dazzling our taste buds with flavour-packed in-flight dining (well, that is the intent) and entertaining us with movies n’ such, there isn’t much left to do, right?


If you’ve been following along, airlines have been focusing on our senses. They’ve got sound, sight, touch and taste down and now it’s time to tackle the last frontier, smell. Airlines have recently been going the way of the celebrity and creating unique scents specific to their brand as an extra measure to chill us out and perhaps even remember them.
Delta's offering is called ‘Calm’, and is sprayed throughout their cabins and infused into their hot towels given out in the front of the plane. What started out as a way of keeping their lavatories smelling fresh and presentable has turned into something bigger and Delta is not alone in their strategy.
United Airlines’ subtle scent, ‘Landing’, is used in their airport lounges with the hope that the orange peel, sandalwood, cedar and leather concoction will eventually become a pleasant association with the brand and indirectly result in more bookings. Continental Airlines and Air Canada’s low-cost brand, rouge, each have theirs and Alaska Airlines (is) currently working towards one.
European airlines are also in the mix, with Turkish Airlines already smelling pretty and plans for Spain’s Iberia to follow suit. Surprisingly, style-heavy Air France and Alitalia have yet to get on board.
Another surprise is that some airlines have been in the scent game for a long time. Take Singapore Airlines, for example. They have been at it for almost 30 years and have not only pioneered the movement but have perfected it to the point that some of their frequent flyers, when blindfolded, can detect the unique smell of the airline and that’s the goal.
Old Spice Claims to be "Better than Nature"

...no doubt with artificial fragrances. Notice the comment about the "evolution of scents having reached its pinnacle." Once again, science is claiming to have improved upon Nature while still returning you to Nature (without ever leaving your urban environment". Somehow, I think they missed the point of being out in Nature!

Saturday, September 20, 2014

In the Land of Lavender

Have you ever had the urge to see for yourself the undulating fields of lavender in Provence?

Valensole Plateau, Provence, France
Row upon row of fragrant beauty disappears into the distance as you bask in the glow of the warm, Mediterranean sun and marvel at the crystal blue canopy above. You inhale deeply as you enjoy the pungent, floral aroma that surrounds you. Does it get any better than this?

I think not!

Any essential oil enthusiast would jump at the chance to travel to the mecca of lavender, and I was no different. This last July, I had the opportunity to visit a childhood friend who has a home in one of the most beautiful hilltowns in the south of France. Much like other medieval towns in the area, St. Paul de Vence is a walled settlement perched on the top of a small mountain behind the city of Nice.

Simiane La Rotonde, Provence
In addition to reconnecting with my friend, I also wanted to participate in a lavender harvest in Simiane La Rotonde, another ancient hilltown situated in one of the most prolific lavender producing areas of Provence: the Valensole Plateau.

This plateau (as you can see above) seems to consist of rolling hills of lavender with a few mountains WAY OFF in the distance, so from scouring many travel books before I left, I naturally thought this was what ALL of the south of France looked like. It was quite a shock when I got there last July to discover that the entire province, and the neighboring Haute  Provence, are filled with small mountains, singularly and in chains (the Alpilles). To travel from place to place often involves traversing twisty, winding roads with traffic that can be slow-going at times. What looks like a straight shot on a map might take twice as long as you planned because it involves navigating hills and valleys, one after the other!

Abbaye de Senanque
The famous Cistercian "Abbaye de Senanque" near the hilltown of Gordes is one of those deceptive places, hidden at the bottom of a valley and not easy to get to. The monks chose this location on purpose because it is quiet and remote. Monks need plenty of solitude, but they also work out in the abbey garden and in the lavender fields (some of the funds for running the abbey come from sales of products made from lavender, including their lavender honey, all of which are available in their store.) People from all over the world visit the abbey to appreciate the simplicity of the architecture and the beauty of the surroundings. Tours are conducted throughout the day but ONLY IN FRENCH.

Standing in the lavender fields near Simiane La Rotonde
I got my wish to participate in a lavender harvest, but it wasn't cultivated lavender. Though my daughter and I visited the fields at the foot of Simiane la Rotonde (above), and had the opportunity to tour the nearby co-op distillery, we arrived on location the day after these fields were partially harvested by the group we were joining. On the day we arrived, they piled into a large bus to drive to a more remote location to harvest wild lavender. We were given sickles and gloves and instructed to carefully cut the lavender in bunches and put them in our bags (also provided). By the end of the morning, we reached the top of the hill that overlooked the Valensole Plateau, where fields of cultivated lavender shared space with delicate, lilac colored Clary Sage.

Enjoying the heady scent of Clary Sage at the top of the hill
The next day, the assistant farm manager, young Nicolas Landel, packed a small copper still with the precious lavender buds that we had previously cut according to his instructions. Because our little group had to leave on the rest of our Provence expedition, we weren't able to obtain a sample of the fruits of our labor until we arrived back in St. Paul.

They sent us a TEENIE bottle of the most delicate, sweet lavender oil, very unlike the essential oil produced by cultivated lavender. The wild plants themselves were leggier and more delicate than their cousins that have plenty of water and sunshine. The fragrance of the essential oil matched the character of the plants from which it came. We were also gifted with a precious spray bottle of equally delicate floral water. Mmmm... feels so good sprayed on my face, but I'm cherishing it and trying to make it last until NEXT summer, when I hope to return to Provence with a group.

Here are some photos of other sites we saw on this, our first trip to Provence:

The lavender Museum in Coustellet

Flower and vegetable market in Nice

View of Nice and the beach from the park above Vieux Nice

Street scene in Grasse
Ancient perfume vials in the Perfume museum, Grasse
Exit door of the perume museum, Grasse
The ancient Roman town of Glanum near St. Remy
My daughter and I strolled out to the end of the half-built bridge across the Rhone river at Avignon. Together we had sung the famous song "Sur le pont d'Avignon, l'on y dance, l'on y dance, sur le pont d'Avignon, l'on y dance toute en rond" when she was a child. What fun to finally see it!

The Bridge of  St. Benezet or Pont D'Avignon
I'll be taking a group with me next year for a week long harvest experience and Provence site-seeing journey. Want to join me? If you'd like to be added to my "I'm interested" list, please contact me at lcmooredc@sbcglobal.net and check out our other trip to Sedona, too at Essential Oil Journeys.

Saturday, October 26, 2013

Tea Tree Oil and Biofilms

by Robert Tisserand (www.roberttisserand.com)

One of the outstanding properties of many essential oils, including tea tree (Melaleuca alternifolia), is that they can be effective even against bacterial biofilms.

A biofilm is a layered matrix, consisting mainly of polysaccharide and protein, that bacteria or fungi create on a surface as a secure habitat. In this form they are more difficult to kill, because the biofilm structure affords protection from the environment. Plaque on teeth is an example of a biofilm and the success of ‘essential oil’ mouthwashes such as Listerine compared to others is partly due to their ability to break down and inhibit plaque formation (Oyanagi et al 2012). (Listerine contains four essential oil constituents: thymol, menthol, 1,8-cineole and methyl salicylate. It was originally developed and used as a surgical antiseptic.)

In a biofilm, the outer layer consists of more or less dormant cells that are also especially resistant. Medical implants, such as heart valves, catheters, stents etc, are becoming more common. They are subject to colonization by bacterial biofilms, and if this occurs the result can be fatal, as antibiotics have great difficulty penetrating the outer layer of resistant bacteria (Hoiby et al 2010). Consequently, implant-related fatalities are on the rise.
S. aureus on a catheter
Carvacrol and cinnamaldehyde (major constituents of oregano oil and cinnamon bark oil respectively) inhibited biofilm formation on a polymer coating. It is proposed that medical devices coated with such compounds would be much less susceptible to bacterial colonization. Cinnamaldehyde significantly reduced Pseudomonas aeruginosa biofilm at 1%, and most bacteria were inhibited by either compound at 0.1% (Zodrow et al 2012). P. aeruginosa is one of the most difficult bacteria to kill. It forms mucosal biofilms in the lungs in cystic fibrosis, and it can be a problem in wound healing.

Biofilm may be found on contact lenses, chronic wounds and ulcers, vaginal mucous membrane, in fact on any surface where there is moisture and nutrients. It is constantly forming on our skin, in addition to the usual mix of dirt, sebum, sweat and cosmetics. Biofilms are also found on surfaces outside the body. Because of a combination of grease-cutting and antibiofilm properties, pine oil and orange oil are common ingredients in household disinfectants. More on biofilms here.

In vitro testing often shows antibiotics to be more effective than essential oils. Conversely, some essential oils are more effective at killing bacteria in biofilm, because they can penetrate it more effectively, and because they are less susceptible to resistant mechanisms. Essential oils that have shown good antibiofilm action in in vitro testing include:

Cinnamon bark: Staphylococcus epidermis biofilm (Nuryastuti et al 2009)
Oregano: S. aureus and S. epidermis biofilm (Nostro et al 2007)
Thyme: Listeria monocytogenes biofilm on stainless steel and polystyrene (Desai et al 2012)
Rosemary: Candida albicans and C. tropicalis biofilm (Chifiriuc et al 2012)
Tea tree: S. aureus, MRSA and C.albicans biofilm (Kwiecinski et al 2009, Park et al 2007, Sudjana et al 2012)

Some of these essential oils are now being considered for use in food preservation, another situation where biofilm formation is a challenge.

M. alternifolia in flower *
Staphylococcus aureus is a ubiquitous bacterium, notably found on the skin. In vitro research shows that tea tree oil dose-dependently eradicates S. aureus biofilm (Kwiecinski et al 2009) and that it is effective against MRSA and MSSA biofilm (Brady et al 2006). A 50% concentration of tea tree oil was as effective as vancomycin in vitro in eradicating MRSA biofilm on typanostomy tubes (Park et al 2007). S. aureus biofilm, in an infected cochlear implant, was found to be resistant to all conventional antimicrobials, but 5% tea tree oil completely eradicated it in one hour (Brady et al 2010). Tea tree oil has shown good effect in eradicating MRSA on the skin, used at 5% in a body wash, in addition to either 4% in an ointment (Caelli et al 2000) or 10% in a cream (Dryden et al 2004).

Candida albicans
forms biofilms that cause disease and are difficult to treat with conventional antifungal agents. At 0.031% in vitro, tea tree oil significantly reduced biofilm formation for all of 10 C. albicans isolates tested (Sudjana et al 2012). Further in vitro work suggests that tea tree oil may be effective in oral hygiene products for the prevention and control of oral candidosis in cancer patients (Bagg et al 2006, Ramage et al 2012). In 25 AIDS patients with oral candidosis who had not responded to fluconazole treatment, 7 were cured and 8 improved after four weeks using oral solutions containing tea tree oil (Vazquez et al 2002).

These studies suggest promising uses for essential oils, notably tea tree, in the prevention and eradication of biofilm-related medical problems that may be resistant to conventional treatment, as well as in surface cleaning, hand hygiene and skin cleansing products.


Bagg J, Jackson MS, Sweeney MP et al 2006 Susceptibility to Melaleuca alternifolia (tea tree) oil of yeasts isolated from the mouths of patients with advanced cancer. Oral Oncology 42:487-492
Brady A, Loughlin R, Gilpin D et al 2006 In vitro activity of tea-tree oil against clinical skin isolates of meticillin-resistant and -sensitive Staphylococcus aureus and coagulase-negative staphylococci growing planktonically and as biofilms. Journal of Medical Microbiology 55:1375-1380 http://jmm.sgmjournals.org/content/55/10/1375.full.pdf+html
Brady AJ, Farnan TB, Toner JG et al 2010 Treatment of a cochlear implant biofilm infection: a potential role for alternative antimicrobial agents. Journal of Laryngology, Rhinology &Otology 124:729-738
Caelli M, Porteous J, Carson CF et al 2000 Tea tree oil as an alternative topical decolonization agent for methicillin-resistant Staphylococcus aureus. Journal of Hospital Infection  46:236-237
Chifiriuc C, Grumezescu V, Grumezescu AM et al 2012 Hybrid magnetite nanoparticles/Rosmarinus officinalis essential oil nanobiosystem with antibiofilm activity. Nanoscale Research Letters 7:209 http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3368737/
Desai MA, Soni KA, Nannapaneni R et al 2012 Reduction of Listeria monocytogenes biofilms on stainless steel and polystyrene surfaces by essential oils. Journal of Food Protection 75:1332-1337
Dryden MS, Dailly S, Crouch M 2004 A randomized, controlled trial of tea tree topical preparations versus a standard topical regimen for the clearance of MRSA colonization.   Journal of Hospital Infection 56:283-286
Hoiby N, Bjarnsholt T, Givskov M et al 2010 Antibiotic resistance of bacterial biofilms.  International Journal of Antimicrobial Agents 35:322-332
Kwiecinski J, Eick S, Wojcik K 2009 Effects of tea tree (Melaleuca alternifolia) oil on Staphylococcus aureus in biofilms and stationary growth phase. International Journal of Antimicrobial Agents   33:343-347
Nostro A, Sudano Roccaro A et al 2007 Effects of oregano, carvacrol and thymol on Staphylococcus aureus and Staphylococcus epidermidis biofilms. Journal of Medical Microbiology 56:519-523 http://jmm.sgmjournals.org/content/56/4/519.long

Nuryastuti T, van der Mei HC et al 2009 Effect of cinnamon oil on icaA expression and biofilm formation by Staphylococcus epidermidis. Applied & Environmental Microbiology 75:6850-6855 http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2772433/

Oyanagi T, Tagami J, Matin K et al 2012 Potentials of mouthwashes in disinfecting cariogenic bacteria and biofilms leading to inhibition of caries. The Open Dentistry Journal 6:23-30http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3269010/
Park H, Jang CH, Cho YB et al 2007Antibacterial effect of tea-tree oil on methicillin-resistant Staphylococcus aureus biofilm formation of the tympanostomy tube: an in vitro study. In Vivo 21:1027-1030 http://iv.iiarjournals.org/content/21/6/1027.long

Ramage G, Milligan S, Lappin DF et al 2012 Antifungal, cytotoxic, and immunomodulatory properties of tea tree oil and its derivative components: potential role in management of oral candidosis in cancer patients. Frontiers in Microbiology 3:22
Sudjana AN, Carson CF, Carson KC et al 2012 Candida albicans adhesion to human epithelial cells and polystyrene and formation of biofilm is reduced by sub-inhibitory Melaleuca alternifolia (tea tree) essential oil. Medical Mycology 50:863-870
Vazquez JA, Zawawi AA 2002 Efficacy of alcohol-based and alcohol-free melaleuca oral solution for the treatment of fluconazole-refractory oropharyngeal candidiasis in patients   with AIDS. HIV Clinical Trials 3:379-385

Zodrow KR, Schiffman JD, Elimelech M 2012 Biodegradable polymer (PLGA) coatings featuring cinnamaldehyde and carvacrol mitigate biofilm formation. Langmuir 28:13993-13999

*Melaleuca alternifolia photo from The Australian Tea Tree industry Foundation

Tuesday, May 28, 2013

ROOTS: German Chamomile and other moderate climate oils

Many of the oils we use on a daily basis in aromatherapy are somehow associated with dry and hot climates or with poor soil. Apparently these stresses induce the plants to produce more powerful essential oils to ensure survival. Examples are Citrus, Lavender and Rosemary oils. The EO’s from these plants employ a chemical vocabulary that is heavily centered on simple monoterpenoid components, such as cineol, terpineol or linalool.

Quite distinct from those are essential oils from many species that belong to the Asteraceae and Apiaceae families. Often these oils find their highest degree of finesse not so much in the hotter subtropical climates but in the moderate and moist climates encountered in Central and Eastern Europe. In the case of German Chamomile the relation between the plant and a specific geography has even become a part of the common name of the species.

For aromatherapy this is quite interesting. These latter plant families thriving in the more moderate climates have evolved to display a more diverse array of components than the essential oils from plant species that developed before them. Lactones and en-yn ethers are just two examples.

In this post I would therefore like to share some thoughts about some classic oils of the daisy (Asteraceae) and the parsley (Apiaceae) family.

German Chamomile
German Chamomile (Matricaria recutita) is one of the best researched medicinal plants. Much of the abundant modern research, dating from the late seventies and early eighties, is ‘pre-internet’ and hence not so easy to locate.

Summing up for the purposes of aromatherapy: Depending on a variety of factors, most importantly genotypes, the Chamomile plant produces chemotypes of essential oil. Some oils have high concentrations of bisabolone and others have high concentrations of bisabolol oxide. However, only a third type, with (-) alpha bisabolol, truly has the full powerful antiinflammative qualities associated with this essential oil. It is a more powerful antiinflammative component than the characterisically blue Chamazulene.

The oil we offer is from an estate in southern Germany specializing in the cultivation and distillation of German Chamomile essential oil. As this is the climate and also the cultural environment where Chamomile has been a part of life for at least a thousand years (Odo Magdunensis, 11. Jh.) it reaches its greatest finesse in the moderate climates of central Europe. Oils from other parts of the world with subtropical climates invariably are of lesser quality.

Yarrow essential oil is distilled in a variety of places, however, demand for it and consequently its production seem irregular. The most relevant quantities on the market are from Eastern Europe with Bulgaria being the main supplier, and to a lesser degree Serbia and Bosnia and Herzegovina.

Wild oils are described as having a concentration of approximately 1% chamazulene and cultivated oils as having a somewhat higher percentage. The wild oils have a light blue tinge whereas the cultivated oils are a darker color blue. Whether the oil with the higher Chamazulene content is really of higher value – therapeutically – remains questionable.

The appreciation of Yarrow essential oil in aromatherapy is probably fueled to a large degree by its traditional popularity in herbalism. As such Yarrow is popular in different ethnopharmacological traditions, even Bedouins in desert areas of the Middle East value Achillea millefolium as an anti-allergy agent and for the treatment of high fever.

In modern aromatherapy Yarrow (Achillea millefolium) essential oil is described as a powerful antiinflammatory agent with particular affinity for rheumatic pain. It is ‘the’ oil to alleviate neuralgic pain and Franchomme and Pénoël even list prostatitis and kidney stones under the indications for Yarrow essential oil.

Some of the components found in Yarrow essential oil are quite special, i.e. the sesquiterpene lactone achilline or its isoartemisia ketone. Considering the appreciation Yarrow has had throughout history it is quite likely that some of its best therapeutic qualities are still to be explored.

Angelica (Angelica archangelica) root essential oil is precious and unique. Unique for its content of musk lactone and musk ketone which give its aroma the much desired exalting fragrance quality. The novice can easily explore this particular quality by creating a simple blend of equal parts of Bergamot, Jasmine absolute, and Angelica.

Therapeutically,  Angelica is an essential oil with great benefits for those who are weakened or asthenic.

Angelica Root essential oil contains a variety of coumarines and furocoumarines which render the oil photosensitizing if used externally, but make it effective to ease anxiety, insomnia and nervous exhaustion and to ease digestive cramping that goes along with these stresses.
Angelica Seed oil has generally similar qualities as the root oil and its musk fragrance is a bit more nuanced than that of the seed oil.

Lovage Root
Lovage Root essential oil is apparently somewhat difficult to produce. The specific gravity of the oil is very near that of water so it rises to the top very slowly. But the unique composition of this essential oil makes it worth the effort to separate this oil from the hydrosol.

Lovage Root essential oil contains a variety of components called phtalides. In a simplified way one could say that the phtalides from Lovage Root remove toxins from the body by chelating them. In the French literature Lovage Root essential oil is recommended for liver congestion, and food, chemical or drug poisoning. Franchome and Pénöel consider it to be one of the most effective agents to treat Psoriasis. The oil  is very powerful and should be explored cautiously.

Hops, being from the Cannabinaceae family do not fit perfectly into this post’s Apiaceae and Asteraceae theme. However, its cultural coordinates are classically central European. Its main actions are quickly described: it is estrogen-mimicking and it is a very fast acting sedative and de-stressing oil. It is especially effective to calm irregular heartbeat and heart arythmia.

Carrot Seed (Daucus carota)
The outstanding therapeutic qualities of Carrot Seed essential oil have been explored in different environments. Recently, however, a study of Anne-Marie Giraud-Robert established the therapeutic value of this essential oil (in combination with some others) for conditions of the liver. The French literature attributes the capacity to regenerate hepatocytes to Carrot Seed oil. The oil’s ability to improve liver metabolism also seems to be the origin of its skin regenerating qualities.

The qualities of Carrot Seed on the market are often uneven as well as in essential oil is distilled from cultivated plants and from plants gathered in the wild. Although their therapeutic properties seem to be more or less identical the wild Carrot Seed oils often have a most appealing and complex fragrance, almost being a perfume in themselves!

Celery Seed 
Celery Seed essential oil (Apium graveolens) is next to Lovage Root the only common essential oil with a sizeable content of detoxifying phtalides. Similarily it drains toxins from the liver. It also acts as a forceful tonic.

From Dr. Kurt Schnaubelt’s blog. Posted in February 2013.

Sunday, April 7, 2013

How Plant Oils Contribute to the Smell of Rain

A recent article in Smithsonian.com illustrates one more way that plants use volatile oils. The story also highlights the connections between plants and humans and how we've co-evolved for our mutual benefit. In our Biology of Essential Oils module, we talk about three reasons that plants make essential oils: 1) To repel predators, bugs, and anything that may do them harm 2) As signalling mechanisms to attract pollinators, warm other plants of impending danger (such as an herbivore that just chomped on one of the plant's leaves), and to appeal to humans who will cultivate them more 3) To protect the plant when it's stressed, such as during drought (plant oils conserve moisture). Read the article below and see if you can pick out another reason plants make essential oils.

What Makes Rain Smell So Good?

A mixture of plant oils, bacterial spores and ozone is responsible for the powerful scent of fresh rain. Image via Wikimedia Commons/Juni
Step outside after the first storm after a dry spell and it invariably hits you: the sweet, fresh, powerfully evocative smell of fresh rain.

If you’ve ever noticed this mysterious scent and wondered what’s responsible for it, you’re not alone.

Back in 1964, a pair of Australian scientists (Isabel Joy Bear and R. G. Thomas) began the scientific study of rain’s aroma in earnest with an article in Nature titled “Nature of Agrillaceous Odor.” In it, they coined the term petrichor to help explain the phenomenon, combining a pair of Greek roots: petra (stone) and ichor (the blood of gods in ancient myth).

In that study and subsequent research, they determined that one of the main causes of this distinctive smell is a blend of oils secreted by some plants during arid periods. When a rainstorm comes after a drought, compounds from the oils—which accumulate over time in dry rocks and soil—are mixed and released into the air. The duo also observed that the oils inhibit seed germination, and speculated that plants produce them to limit competition for scarce water supplies during dry times.

These airborne oils combine with other compounds to produce the smell. In moist, forested areas in particular, a common substance is geosmin, a chemical produced by a soil-dwelling bacteria known as actinomycetes. The bacteria secrete the compound when they produce spores, then the force of rain landing on the ground sends these spores up into the air, and the moist air conveys the chemical into our noses.

“It’s a very pleasant aroma, sort of a musky smell,” soil specialist Bill Ypsilantis told NPR during an interview on the topic. “You’ll also smell that when you are in your garden and you’re turning over your soil.”

Because these bacteria thrive in wet conditions and produce spores during dry spells, the smell of geosmin is often most pronounced when it rains for the first time in a while, because the largest supply of spores has collected in the soil. Studies have revealed that the human nose is extremely sensitive to geosmin in particular—some people can detect it at concentrations as low as 5 parts per trillion. (Coincidentally, it’s also responsible for the distinctively earthy taste in beets.)

Ozone—O3, the molecule made up of three oxygen atoms bonded together—also plays a role in the smell, especially after thunderstorms. A lightning bolt’s electrical charge can split oxygen and nitrogen molecules in the atmosphere, and they often recombine into nitric oxide (NO), which then interacts with other chemicals in the atmosphere to produce ozone. Sometimes, you can even smell ozone in the air (it has a sharp scent reminiscent of chlorine) before a storm arrives because it can be carried over long distances from high altitudes.

But apart from the specific chemicals responsible, there’s also the deeper question of why we find the smell of rain pleasant in the first place. Some scientists have speculated that it’s a product of evolution.

Anthropologist Diana Young of the University of Queensland in Australia, for example, who studied the culture of Western Australia’s Pitjantjatjara people, has observed that they associate the smell of rain with the color green, hinting at the deep-seated link between a season’s first rain and the expectation of growth and associated game animals, both crucial for their diet. She calls this “cultural synesthesia”—the blending of different sensory experiences on a society-wide scale due to evolutionary history.

It’s not a major leap to imagine how other cultures might similarly have positive associations of rain embedded in their collective consciousness—humans around the world, after all, require either plants or animals to eat, and both are more plentiful in rainy times than during drought. If this hypothesis is correct, then the next time you relish the scent of fresh rain, think of it as a cultural imprint, derived from your ancestors.


Did you see it? Another reason for plants to secrete essential oils: "the oils inhibit seed germination, and speculated that plants produce them to limit competition for scarce water supplies during dry times." And one more. The compound called geosmin lets us humans know that Spring is coming and soon we will have more plant and animal food available to us. Another evolutionary link between plants and humans. Thank you, plants!


Above article from Smithsonian.com, Surprising Science, posted April 2nd by Joseph Stromberg.