The Essential Oil Question Almost No One Asks

In over twenty years of teaching animal aromatherapy, I've noticed something curious: almost no one asks which rosemary they should use for their animal companion. Most pet parents don't even know there is more than one.

One of my students in the course at Essence of Thyme College of Holistic Studies recently ran into this exact gap, needing some guidance to understand why two rosemary essential oils could behave so differently, despite sharing a bottle label and a botanical name.

The difference comes down to two concepts pet parents rarely hear about: chemotypes and species. Understanding both is one of the simplest, most important ways to keep your animal friend safe while choosing essential oils that truly support them, rather than overwhelm them.

What Is a Chemotype?

A chemotype (abbreviated "CT") is a chemical variation within the same plant species. The plant looks the same, grows the same, and carries the same botanical name, but depending on climate, soil, and growing conditions, it produces a different dominant chemical makeup, and therefore a different essential oil.

Most essential oils don't have chemotypes at all.  But when a chemotype does exist, you'll usually see it noted right in the oil's name, with "CT" followed by the dominant chemical constituent.

There are four essential oils with chemotype variations that pet parents should know:

• Lemongrass CT Rhodinol (Cymbopogon citratus)
• Rosemary CT 1,8-Cineole (Salvia rosmarinus)
• Rosemary CT Verbenone (Salvia rosmarinus)
• Thyme CT Linalool (Thymus vulgaris)

Take rosemary as an example. Rosemary CT 1,8-Cineole shines for respiratory support,  a strong, stimulating oil that's too much for a sensitive animal companion.  Rosemary CT Verbenone is the gentler starting point for our animal companions.

If I'm supporting a dog through kennel cough, for example, I'll start with Rosemary CT Verbenone and only move to Rosemary CT 1,8-Cineole if more respiratory support is needed. I also like to offer both oils and let the dog self-select, animals often have a clear preference, and that instinct is worth trusting.

This is why, when a chemotype option exists, I always reach for the mildest one first when working with animals. Their bodies simply aren't built to process the same intensity ours can.

What's the Difference Between a Chemotype and a Different Species?

Here's where it gets a little more interesting, and honestly, a little more important to understand.

A chemotype is a variation within one species. But plants in the same family can also include multiple, entirely different species, each with its own distinct Latin binomial (that italicized scientific name you'll sometimes see in parentheses). These aren't variations of one plant. They're different plants altogether that happen to share a common name or family.

Cedarwood is a perfect example. When someone says "cedarwood essential oil," they could be talking about any of these:

• Atlas Cedarwood (Cedrus atlantica)
• Indian/Himalayan Cedarwood (Cedrus deodara)
• Virginian Cedarwood (Juniperus virginiana)

This isn't just a technical distinction, it shows up in how you'd actually use these oils. The Cedrus genus (Atlas and Himalayan Cedarwood) tends to be more calming and grounding, a lovely choice for an anxious dog or a cat who startles easily. It's worth knowing that Atlas Cedarwood has been overharvested to the point of being considered at risk, so I lean toward Himalayan Cedarwood or a responsibly sourced supplier when I want that calming profile.

The Juniperus genus (Virginian Cedarwood) leans a different direction entirely, it's one of the essential oils I reach for to help repel insects. Even the scent tells the story: Atlas and Himalayan Cedarwood share a similar soft, woody-sweet aroma, while Virginian Cedarwood carries that classic, sharper cedar-wood scent most people picture when they hear "cedar." Same common name, but three different plants, with different aromas and different roles in your natural remedy toolkit.

Notice that these aren't even in the same genus, in cedarwood's case, we're talking about two entirely different plant genera (Cedrus and Juniperus) sharing one common name. That's a very different situation from a chemotype, and it's exactly why relying on a common name alone can lead you astray. The gap actually runs even deeper than genus. Cedrus belongs to the pine family (Pinaceae), while Juniperus belongs to the cypress family (Cupressaceae), two entirely different plant families. So "cedarwood" on a label can mean plants that aren't just different species, but different genera, in different families altogether.

If you'd like to go deeper on choosing between cedarwood oils, I walk through it in this video: Which Cedarwood Essential Oil Should You Choose?

The genus story goes even deeper than that. Juniper Berry (Juniperus communis) shares the same genus as Virginian Cedarwood, yet it's a completely different essential oil, in both chemistry and in how it's made. Cedarwood oils, Virginian Cedarwood included, are steam distilled from the wood or sawdust shavings. Juniper Berry essential oil comes from distilling the berries themselves. Same genus, different plant part, different process, and a very different oil.

Chamomile works the same way, though the gap here is a little narrower:

• German Chamomile (Matricaria recutita)
• Roman Chamomile (Chamaemelum nobile)

The same pattern shows up here too. Roman Chamomile tends to be more calming, a good fit for an anxious animal companion who needs to settle. German Chamomile is highly anti-inflammatory, making it a go-to for easing pain, especially for aging dogs who are restless alongside their discomfort. Same "chamomile" name, two different jobs.

Unlike cedarwood, though, German and Roman Chamomile share the same plant family, Asteraceae, just different genera. So "same name behind different plants" can mean anything from a shared family down to, as we saw with rosemary, a shared species. There's genuinely more behind that name on the bottle than most of us were ever taught to look for.

Why This Matters So Much for Our Animal Companions

Our dogs and cats process essential oils differently than we do. Their heightened sense of smell, their body size, their liver, all of it means the margin for error is smaller. An essential oil that's simply "strong" for a person could be genuinely too much for our animal friends.

When you know to read the label and look for the Latin binomial, you're equipped to make a more informed, gentler choice for your animal friend. It's a small habit that makes a real difference.

Frequently Asked Questions

Do all essential oils have chemotypes? No. Chemotypes are the exception, not the rule. Most essential oils don't have chemical variations within the same species. When they do exist, they're typically labeled with "CT" plus the dominant constituent.

How can I tell if an oil I already own has a chemotype? Check the label for "CT" followed by a chemical name (like "CT Verbenone"). If it's not there, the oil likely doesn't have a documented chemotype, though it's always worth confirming the specific species with the supplier.

Is a milder chemotype always safer for my pet? Milder generally means gentler on the body, which is often a good starting point for animals, especially those who are elderly, sensitive, or new to essential oils. That said, "gentler" isn't the same as "risk-free." Proper dilution and species-appropriate use still matter.

Why do different species share the same common name? Common names were created for convenience, long before modern botanical classification. Many were named based on similar scent, appearance, or regional use, even when the plants aren't closely related botanically.

Understanding chemotypes and species won't just make you a savvier essential oil shopper. It will help you become a more confident, informed advocate for your animal companion's wellbeing, one gentle, educated choice at a time.