Blending essential oils is part art, part science, and part lived experience. As aromatic expert John Steele beautifully puts it, creating blends is “learning to listen through your nose.”

A foundational concept in fragrance blending is the molecular weight of essential oils. Lighter, less viscous oils have smaller molecules, making them more volatile and aromatic. These oils evaporate quickly, disperse rapidly in the air, and absorb into the body faster—meaning their scent fades more quickly. In contrast, heavier, more viscous oils contain larger molecules, which makes them less volatile. They evaporate more slowly and remain on the body and in the air for a longer time.

What’s particularly exciting about molecular weight is how it contributes to synergy in a blend. Heavier oils can act as “anchors,” allowing the lighter, more fleeting aromas to last longer. This phenomenon is known in perfumery as the “fixative effect,” a kind of molecular buddy system that creates balance and longevity in aromatic profiles.

The familiar terms “top,” “middle,” and “base notes” are rooted in the volatility and molecular structure of essential oils:

• Top notes are highly volatile and evaporate first. They’re the initial scent that greets the nose—bright, fresh, and fleeting.
• Middle notes give the blend its heart and character. They emerge after the top notes fade and evaporate at a moderate rate.
• Base notes are the most enduring. They evaporate slowly, linger longest, and often function as natural fixatives in a formula.

Although many oils are categorized into a primary note, most essential oils contain components that touch on all three note levels—top, middle, and base—contributing to their complexity and versatility.

The varying molecular weights of essential oils also underscore why it’s critical to measure by weight rather than by drops when blending essential oils. One drop of a thick, heavy oil like patchouli can weigh significantly more than a drop of a light oil like lemon, which can drastically affect the balance and potency of your blend.

When crafting an aromatherapy blend, one of the most important decisions is whether your goal is scent, therapeutic function, or both. If you’re blending for therapeutic effect, begin by choosing oils that match your intended outcome. Then layer in additional oils that support those properties while also creating a pleasing and well-rounded aroma.

Ultimately, great blending requires an appreciation for the subtlety of single notes and the harmony they create together. Trust your nose, honor your purpose, and let the oils guide the experience.

To learn more about essential oils we recommend The Art, Science and Business of Aromatherapy: A Guide to Essential Oils and Entrepreneurship by one of our founders, Kayla Fioravanti and The Unspoken Truth About Essential Oils by Kayla Fioravanti, Stacey Haluka, with Adverse Reaction Report by Robert Tisserand, Conclusions by Martin Watt, Forward by Dr. Robert Pappas, and Epilogue by Sylla Sheppard-Hanger.