Inside Baseball: The Design of Olfactory Studies

You throw the ball, you hit the ball, you catch the ball

Can smelling a “proprietary essential oil blend” consisting of thyme, orange, clove bud, and frankincense boost energy levels among people suffering from the fatigue of long COVID? Interesting question. One that a recent study by Hawkins et al. set out to investigate using a “randomized double blind, placebo controlled trial.”

Sounds impressive! So what did patients in the placebo condition sniff? A random food odor, maybe? Another blend of oils, perhaps one designed to induce relaxation? Nope. Neither.

The placebo condition had patients sniff “an inert, odorless fractionated coconut oil.” In what way is an odorless oil a control for a scented oil? It isn’t. The very act of repeatedly sampling an odor has consequences in sensory adaptation, psychological expectation, etc. To control for the effects of just smelling something, you need a different—presumptively non-efficacious—smell. A no-odor condition can serve as a baseline comparison for the test odor, but there needs to be an alternative-odor control condition as well. A no-odor control by itself is worthless, and as a result the entire study by Hawkins et al. is a waste of time.

The Battle of the Appropriate Control Group was fought back in the aromatherapy wars of the 1990s. The Odorless Control forces were decisively routed. A generation later there is no excuse for this kind of slipshod experimental design. The reviewers and editor of this paper should be ashamed of themselves. [Forget it, Jake, it’s alternative medicine.—Ed.]

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Jessie Hawkins, Christy Hires, Lindsey Keenan, and Elizabeth Dunne. (2022). Aromatherapy blend of thyme, orange, clove bud, and frankincense boosts energy levels in post-COVID-19 female patients: A randomized, double-blinded, placebo controlled clinical trial. Complementary Therapies in Medicine 67:102823.