Aromatherapy: Exploring Olfaction

Spas and lotions claim that aromatherapy can work all sorts of wonders, from reducing pain and anxiety to enhancing energy and short-term memory. An alarming number of companies and websites even claim that it can even prevent hair loss. But before you go lather yourself in essential oils, does aromatherapy actually work?

Aromatherapy is the use of fragrance to enhance health and promote feelings of well-being. This “aroma” usually comes from essential oils or concentrated aromatic liquids extracted from plants. You probably recognize the smell of common aromatherapy scents from your hand soap, such as jasmine, rosemary, and lavender. You have also probably heard that each scent can influence your body in different ways. For example, the lavender scent in your hand soap is supposed to relieve stress and calm the body.

Though the term “aromatherapy” did not appear until the early 1900s, the concept has been around for thousands of years. Egyptians used odors to treat diseases, and the Greek physician Dioscorides even wrote books on essential oils and their healing properties. Today, aromatherapy is popular not only in spas but also as a way to relieve labor pains, reduce chemotherapy side effects, and promote restful sleep.

Few reliable scientific studies have been conducted, but a study from the Mie University School of Medicine found that patients with depression needed smaller doses of antidepressant medications after citrus fragrance treatment. Another study from the University of Vienna demonstrated that when the scent of orange oil was used in dental clinics, female patients exhibited decreased anxiety. These studies suggest that some fragrances may have a clinically quantifiable effect on mood.

While there may be evidence for aromatherapy’s mood altering effects, scientific proof for physiological improvements is lacking. Most of the evidence for reducing pain and decreasing healing times is anecdotal rather than scientifically grounded. In fact, a recent study at Ohio State University found that aromatherapy did not cause any physiological effects. While lemon oil did improve moods, neither lemon oil nor lavender significantly changed pain ratings, heart rate, blood pressure, wound healing, or stress hormone levels. The lack of physiological response to lemon oil and lavender, two of the most popular scents, seems to indicate that aromatherapy does not provide all the health benefits that spas and other essential oil businesses often claim.

Yet there is something to be said for the consistent mood improvement across studies. When you smell lemon oil, some molecules dissolve in the mucus lining of the olfactory epithelium on the roof of the nasal cavity. There, the molecules stimulate olfactory receptors. Olfactory sensory neurons carry the signals from the receptors to the olfactory bulb, which filters and begins processing the input signals of the lemon scent. Mitral cells then carry the output signals from the olfactory bulb to the olfactory cortex, which allows you to perceive and recognize the tangy scent of lemon.

Interestingly, the mitral cells do not only lead to the olfactory cortex, they also carry the signals from the lemon scent to other areas in the brain’s limbic system. Some mitral cells connect directly to the amygdala, the brain structure involved in emotional learning and memory. Indeed, the olfactory system is the only sensory system that involves the amygdala and the limbic system in its primary processing pathway. This link explains why smells are often linked to specific memories. For example, if you have had a positive experience with lemon meringue pie, the scent of lemon may induce positive thoughts.

A simplified diagram of the olfactory system. Notice the wispy scent entering through the nostrils stimulating the olfactory bulb, which sends electric impulses to the limbic area. Image courtesy of Doriew.

Another explanation for mood improvements and the reported pain reduction may be the placebo effect. According to this theory, an individual’s expectancies, rather than the scent’s characteristics, determine the effects of the scent. Several studies conducted at the Monell Chemical Senses Center found that subjects who were informed that an odor would improve performance achieved better results in a series of math calculations. These studies show that people’s expectations about odors have the power to affect their health and behavior. Thus, scents that are perceived as positive may actually induce their positive effects due to the placebo effect.

Aromatherapy may not have been proved to reduce pain, promote health, or prevent hair loss, but at the very least, it can improve your mood. So do not be too skeptical of the claims of essential oil products because as long as you believe in the powers aromatherapy, you can still reap many of the benefits and justify that spa membership.