The problem with the placebo effect is that it is regarded by most people as a nuisance or a fake. But it isn't

Dr Richard Tonkin, Research Council for Complementary Medicine

The researchers tested oils which were supposed to make people feel more alert.

Volunteers wore surgical masks, some of which were sprayed with essential oil and others with plain water.

The researchers found there was no significant difference in reaction times between people given the aromatherapy oil, and those given water.

The results imply that aromatherapy causes a placebo effect - where patients actually become healthier when they believe they have been given a wonder treatment.

Jasmine

The oils tested came from peppermint, jasmine and ylang-ylang. All are commonly used by aromatherapists to increase alertness.

When the volunteers were asked to rate how stimulating, strong or pleasant they found each spray, those who gave high ratings showed better reaction times.

The researchers say this shows that if people think an oil is stimulating, they get faster.

They now plan to test the effectiveness of massaging the oils into the skin, to see if there is any effect when they are absorbed, rather than inhaled.

Dr Richard Tonkin, of the Research Council for Complementary Medicine, said aromatherapy was a useful technique.

He said: "The power of suggestion is a big factor in all medicine.

"The problem with the placebo effect is that it is regarded by most people as a nuisance or a fake. But it isn't.

"It is a practical and positive effect that acts by catalysing the self-healing mechanisms within a patient."

The aromatherapy market is worth �24m a year in the UK.