If you’ve ever lit a scented candle to help yourself relax after a long day, you may not be surprised to learn that the smell of lavender can help calm stressed horses.

Researchers at the University of Arizona measured cardiac parameters in eight dressage horses before, during and after they inhaled humidified lavender essential oil. Each of the horses was also tested with plain water to serve as a control either one week before or one week after the lavender trial. The experiment was then repeated with the chamomile essential oil.

During the study periods, the horses wore monitors that collected data on heart rate as well as heart rate variability (HRV), the time intervals between heartbeats. HRV is an indicator of the parasympathetic response of the nervous system, and HRV data can be used to produce a measure called “root mean square of successive differences between the intervals” (RMSSD), which increases when a horse is relaxed.

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In the lavender trials, RMSSD scores were higher in seven of the study horses, while in the chamomile trials, only two of the eight horses showed an increase. Horses inhaling the lavender also had significant increases in HRV while those inhaling chamomile showed variable HRV effects, none of which reached statistical significance.

The researchers note that different individuals may be more or less sensitive to lavender or chamomile. In addition, they emphasize that the horses were not subject to any external stressors during the study periods and any physiological effects subsided when inhalation of the essential oil stopped. 

They call for further research “into the molecular basis of the essential oils and the pharmacological activity they produce … to understand how to optimize their effects on individuals, both equine and human.”—Gulsah Kaya Karasu, DVM

Reference: “Effect of Aromatherapy on Equine Heart Rate Variability,” Journal of Equine Veterinary Science, September 2018

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