Lesson 18: Chemistry

Leiann’s Video

YouTube Videos

Required Reading

Foundational Aromatherapy, 1st edition pages 10-14

Foundational Aromatherapy, 2nd edition pages 10-15

Basic Chemistry of Aromatherapy

Why do you need to know about the chemistry of essential oils if you just want to know what oils to use for your runny nose?

When I was in high school I took chemistry after only two whole weeks. I dropped out for three reasons. How many? Three. First, I could not see any value to it for my everyday life. Second, I burned myself badly putting my finger in melted sulfur–I am extremely curious (and we all know what curiosity did to the cat). Finally, and most important for me at the time, there was only one cute boy in the class—but he already had a girlfriend.

In preparing this section, I wanted to make sure I addressed at least the first two issues for you. I want you to see the value these have for you and I don’t want you to get burned! Though I cannot provide a cute boy, you could sit by your significant other or a picture of Elvis or Marilyn Monroe while reading this. That will take care of number three.

How can learning chemistry apply to your everyday life? How can learning chemistry keep you from being burned?

Here is a simple way to become familiar with the basics of essential oil chemistry.

Essential oils can be divided into 10 main groupings. Learning the main things that each of these chemical families do in your body will help you when choosing which oil you want to use. Also useful for answering the question, why did Leiann or someone else put this oil in this particular blend, or how can I make my own blend to do what I want it to do, and have it be both safe and effective.

Let’s learn the ten chemical families. We should have ten fingers or toes, so you should be able to get this down with a few little tricks to help remember. In the table below are the ten main chemical families in alphabetical order, each with a memory-key word to go with it.

Ten Main Chemical Families Memory Key
Aldehydes Aunt
Esters Esther
Ethers excitedly
Ketones kept
Monoterpenes money
Monoterpenols medals
Oxides open
Phenols phones
Sesquiterpenes safely
Sesquiterpenols stored

Memorize: Aunt Esther excitedly kept money, medals, open phones safely stored!

Ten Main Chemical Families

Now we will go over what each chemical family generally does in or to the body, the safety precautions associated with each one, and which oils are in each family. Then we will put it all into a story so you can always remember.

1. Aldehydes

Properties: Sedative or calming to the nervous system, anti-inflammatory, cooling, antifungal. Citrus, lemony smell. Middle note.

Oils: cinnamon bark, eucalyptus citriodora, lemongrass

Safety Notes: Aldehydes can be irritating to the skin and mucous membranes, especially if oxidized. Dilution is important. In fact, oils with aldehydes are considered more effective when diluted, especially for their antispasmodic and sedative effects. You might want to consider using them with skin-friendly oils.

Shelf Life: Aldehyde-rich essential oils is two to three years.

2. Esters

Properties: Sedative, balancing, and soothing to the sympathetic nervous system, emotionally uplifting and stress relieving, antispasmodic (especially digestive cramping). Anti-infectious, healing to the skin (especially for skin irritations). Esters are either floral or fruity in aroma and are usually middle notes.

Oils: bergamot, birch, Roman chamomile, clary sage, fir (balsam), geranium, helichrysum, jasmine, lavender, black spruce, ylang ylang

Safety Notes: There are generally no safety concerns for these oils when properly diluted for the skin. Birch is the exception; it should not be used by pregnant or breastfeeding women, or people with asthma, aspirin sensitivities, or clotting disorders.

Shelf Life: Ester-rich essential oils is three to five years.

3. Ethers

Properties: Antispasmodic, anti-infectious, carminative (reduces flatulence or intestinal gas), pain relieving in the digestive system and genitourinary tract. Licorice-type aroma. Middle notes mostly.

Oils: anise, fennel, dill seed, nutmeg

Safety Notes: Dilute these oils as they can burn the skin. Avoid use during pregnancy, while breastfeeding, or in cases of endometriosis and estrogen-related cancers. Toxicity concerns, in large doses. Check individual oil profiles for specific concerns.

Shelf Life: Ether-rich essential oils is three to five years.

4. Ketones

Properties: Carminative (reduce intestinal gas), pain relieving, expectorant (mucus removing), and improves circulation. Middle notes except vetiver, which is a base note. Different aromas.

Oils: peppermint, spearmint, vetiver

Safety Notes: Not all ketones have the same safety cautions. Peppermint should not be used in high amounts with young children, those pregnant, or people taking high blood pressure medications.

Shelf Life: Ketone-rich essential oils is three to five years.

5. Monoterpenes

Properties: Decongesting to muscular and respiratory systems, enhances skin penetration, warming (helps with pain and stiffness), antiseptic, antiviral, and air purifier. Citrus oils are top notes, others are middle notes. Variety of aromas.

Oils: bay laurel, black pepper, bergamot, cypress, frankincense, fir (balsam), grapefruit, juniper berry, lemon, marjoram, neroli, nutmeg, orange, rosemary, black spruce, tea tree, thyme linalool, tanacetum annuum, cajeput, helichrysum, green mandarin, spearmint

Safety Notes: If they become oxidized from not keeping the lid on tight or stored in a cool dark place, they can cause skin sensitization or irritation. Always use with bath salts for a bath or with a carrier oil as they are lack water solubility.

Shelf Life: Monoterpene-rich essential oils is one to three years.

6. Monoterpenols

Properties: Emotionally balancing, immune stimulant, anti-infectious, healing for the skin. Floral aroma and most are middle notes.

Oils: basil, clary sage, coriander, geranium, lavender, lemongrass, sweet marjoram, neroli, palmarosa, peppermint, rose, rosewood, tea tree, thyme linalool, ylang ylang

Safety Notes: These are generally regarded as safe with no skin irritation. The only exception is peppermint which should not be used on children under the age of five.

Shelf Life: Monoterpenol-rich essential oils is three to five years.

7. Oxides

Properties: Strong respiratory decongestant, mentally stimulating, antiviral, pain relieving or numbing agent, and smells camphor-like.

Oils: bay laurel, German chamomile, eucalyptus globulus, eucalyptus radiata, spike lavender, rosemary 1.8 cineole

Safety Notes: Care must be taken with cineole as it can trigger an attack with asthmatics. Also care should be taken with children under 10. Do not use on infants.

Shelf Life: Oxide-rich essential oils is one to four years.

8. Phenols

Properties: Great immune stimulants, antibacterial and very anti-infectious, stimulates body systems, very spicy, and pungent aroma. Usually a top/middle note.

Oils: clove bud, oregano

Safety Notes: Oils high in phenols are very hot oils and very irritating to the skin. They must be diluted substantially before applying to the skin, usually only 5 to 6 drops per ounce of carrier oil. They are never to be used on babies or young children. Avoid applying to sensitive skin or damaged skin. Clove bud should be avoided by individuals on blood thinners. Never use them in a bath.

Shelf Life: Phenol-rich essential oils is three to five years.

9. Sesquiterpenes

Properties: Anti-inflammatory, antihistamine (remove effects from allergies), antibacterial, antiseptic (germ killing), antispasmodic. A base or middle note and tend to be a heavier oil, making it more calming and centering. They have the longest shelf life and the aroma is also longer lasting. These oils actually have a wide range of properties and aromas, and so it is best to look at the profiles of each individual oil.

Oils: black pepper, cedar wood, ginger, helichrysum, myrrh, patchouli, ylang ylang

Safety Notes: These oils are considered skin safe and non-irritating.

Shelf Life: Sesquiterpene-rich essential oils is six to eight years (usually longer).

10. Sesquiterpenols

Properties: Anti-inflammatory, grounding, cooling, a tonic to the whole body, enhancing the body systems and the mind. Like the sesquiterpenes, you do have to look at each oil’s profile to see the specific properties and aromas. These oils are heavier, a base note, and have a longer shelf life.

Oils: carrot seed, sandalwood, patchouli, cedarwood

Safety Notes: Considered generally safe.

Shelf life: Sesquiterepenol-rich essential oils is six to eight years (usually longer).

Aunt Esther—A Story to Help You Remember

Here’s a story to help you remember the phrase Aunt Esther excitedly kept money, medals, open phones safely stored!

Aunt – Aldehydes

Aunts are like the aldehydes in that a little goes a long way; you need to dilute (limit) your time with them otherwise they will be severely irritating or put you to sleep with their gossip. In small doses, an aunt can be very pleasant to have around; she can calm down inflammatory situations; for example, she can help cool everyone’s tempers.


This particular aunt’s name is Esther. She is everyone’s favorite. She is fun to be around and smells floral and fruity. She always makes everyone feel better, physically or emotionally, whether you have a tummy ache or are just feeling sad. If someone rubs you (your skin) the wrong way or gets your dander up, “Ester” is the one to call.


If Aunt Esther has spasms, digestive pain, urinary tract infections, or just plain old gas, she gets pretty excited. She eats the wrong things all the time, so this happens to her a lot. She is careful not to get too hot when she gets excited.

Kept – Ketones

If the Ether oils don’t help her tummy, the Ketones will help keep her happy. Ketones also help her if she has a headache or a minor injury, like a smashed finger.


Both words include an eee sound at the end, making them e-e-easy to remember. Aunt Esther has a lot of money, and in this family there are many oils. Just like money, these oils need to be protected in a cool dark place like a bank vault. If we don’t keep our money safe, it won’t last as long. Money can help get us out of trouble in many ways.


Both words end in the al or ol sound. Medals make us feel good, and most people get one for protecting others. We don’t have to be quite as worried about protecting our medals as our money.     

Open – Oxides

These oils are all about getting or keeping things open—whether it is your lungs or your mind. These are all about getting oxygen in.


Phenols are like phones in many ways. They are very useful tools and can help you get what you want or need. Phones can also be very irritating if you use them too much for too long, the phone gets hot, you get a headache, etc. If an annoying person keeps calling you, it is wise to take phone calls in small doses. In an emergency,  you want a phone and phenols to aid in the rescue.                   


Both words include with an eee sound at the end, making them also e-e-easy to remember. These oils have no cautions. They are very safe to use and have a long shelf life. Safely is the best word for them: you can safely store these oils in many different ways, and these oils help us in many different ways.


Both words have an “o” in them. Aunt Esther stored these oils in the ground—because they are grounding. It is cool in the ground and they are also cooling oils. They are safely stored because they are very safe—like the previous Safely Stored Sesquiterpene oils.

So there you go! Learn the short sentence and the reminders. When you are looking at the oil profiles and see the chemical families section, you will have a good idea of what that oil can do for you as well as any safety precautions. This information will help you create blends to target certain conditions. For example, to open things up, use oxides; for anti-inflammatory results, use sesquiterpenes; maybe mix some skin friendly oils with some hot ones.

Tada! You are on your way to being a master blender!

Passport to Aromatherapy Pages 10-11