A recent US study on a small group of people found that aromatherapy oils had no physiological effect although they may improve mood for some people.

The study is the work of researchers at Ohio State University and appears in the April issue of the journal Psychoneuroendocrinology.

Described by a doctor speaking on the CBS News Early Show on Tuesday as one of the few studies to take “a very scientific look at aromatherapy”, the study found that the two most popular aromatherapy oils, lemon and lavender, failed to show any improvement in wound healing, immune status, blood pressure, stress hormones, or pain control.

Lemon oil did show a small effect in mood improvement, but lavender oil was even less effective than water, said the researchers who conducted three psychological tests as well as examining physiological effects.

Lead author of the study and professor of psychiatry and psychology at Ohio State University, Dr Janice Kiecolt-Glaser, and colleagues, looked for physiological evidence that the two oils went beyond increasing pleasure. Aromatherapy is a large industry that markets oils as having health benefits, but there is little scientific evidence of this.

Kiecolt-Glaser said:

“We all know that the placebo effect can have a very strong impact on a person’s health but beyond that, we wanted to see if these aromatic essential oils actually improved human health in some measurable way.”

Lemon and lavender are the two most used scents in aromatherapy, and recent research also selected these to study.

The researchers invited 56 healthy male and female volunteers and screened them to find out how good their sense of smell was. Some of the participants believed aromatherapy was effective while the others had no opinion one way or the other.

The participants attended three half day events where they had cotton balls with lemon oil, lavender oil or distilled water taped below their noses while they were examined using a range of physiological and psychological tests.

Their blood pressure and heart rate was monitored during the sessions, and they also gave blood samples. Ability to heal was assessed by a standard test where sticky tape is applied and then removed repeatedly on an area of skin, and reaction to pain was measured from immersing their feet in ice cold water.

The volunteers also completed three standard psychological tests to assess mood and stress at three times during each session. They were also asked to express their reaction to the experience, and their use of positive and negative words in their narrative was assessed.

Several biochemical markers were tested in the blood samples to establish changes in immune and endocrine system. These included the cytokines Interleukin-6 and Interleukin-10, and the stress hormones cortisol, norepinephrine and other catacholomines.

The results showed that while lemon oil clearly enhanced mood, lavender oil had no such effect, and neither smell made any impact on any of the measures for stress, pain control and wound healing.

The study is one of the most comprehensive pieces of research to look at aromatherapy, but the human body is “infinitely complex” said co-author Dr William Malarkey, professor of internal medicine at Ohio State University.

“If an individual patient uses these oils and feels better, there’s no way we can prove it doesn’t improve that person’s health,” he said.

“But we still failed to find any quantitative indication that these oils provide any physiological effect for people in general,” added Malarkey.

Fellow co-author Dr Ronald Glaser, a professor of molecular virology, immunology and medical genetics at Ohio State, said that the wound healing experiment measured how fast the skin repaired itself, and a lot of things have to happen in the body for that to take place:

“We measured a lot of complex physiological interactions instead of just a single marker, and still we saw no positive effect,” said Glaser.

Speaking on the CBS Early Show, Dr Roshini Raj of New York University Medical Center said that the effect of lemon on mood “shouldn’t be underestimated”, saying it was a “pretty good thing” if just smelling something can make a person feel better. Perhaps there is a strong placebo effect, she said, where people believe aromatherapy works but there is no real physiological effect.

She suggested that perhaps some people feel less stressed when they use aromatherapy, and this helps them deal with certain medical conditions.

Raj pointed out that the study was relatively small, and therefore “you can’t say aromatherapy doesn’t work for everyone”.

The message appears to be that while it probably won’t do any harm, and maybe worth a try, don’t expect aromatherapy to replace needed medications.

“Olfactory influences on mood and autonomic, endocrine, and immune function.”
Janice K. Kiecolt-Glaser, Jennifer E. Graham, William B. Malarkey, Kyle Porter, Stanley Lemeshow and Ronald Glaser.
Psychoneuroendocrinology Volume 33, Issue 3, April 2008, Pages 328-339.

Click here for Abstract.

Source: CBS News, Science Daily, journal abstract.

Written by: Catharine Paddock, PhD