Flower scents sprayed around the bedroom before sleep result in more positive dreams than unpleasant smells or no odours at all, according to new research.
But although bedtime aromas influence the type of dreams people have, actual smells feature in the plots of less than one in 100 dreams. What we dream most about are everyday concerns and interests like friends, driving, shopping and sport.
Our sense of smell may not be as good as that of most animals: there are around five million receptor cells in the human nose compared to 200 million in a dog’s nasal passages, but it has a major role in the emotions and in both physical and mental health.
It’s thought that the significant effects of smell on the brain are a relic of the life-and-death importance that smell had for early man. Those smell cells in the nose are linked to the limbic system - which in evolutionary terms is among the oldest parts of the brain - which governs emotions, behaviour and long-term memory.
Sense of smell is also controlled from here, and in primitive man this sense would have been much more powerful, helping him to sniff out both enemies and food. But although the survival importance of smell has largely disappeared, its effects on the brain and body remain.
As research is increasingly showing, smells can impact on almost everything, from dreams and emotions, driving, stress and gambling, to pain, concentration, memory and romance. While a whiff of lavender releases feel-good hormones and makes us happier, the scent of roses lowers blood pressure and a hint of eucalyptus improves alertness.
How smell affects spending
Smells can have an effect on what we buy, how much we spend, and even on what we gamble. In one study based at a Las Vegas casino, there was a near 50 per cent rise in money gambled when a pleasant scent was sprayed around slot machines. Researchers at Chicago University found that 84 per cent of shoppers found identical new shoes more attractive when they were displayed in a room with a pleasant aroma compared to one with no smell. They also valued the shoes at £10 more.
How smell affects dreams
Smelling flowers before sleep can lead to more positive dreams. In research at the Sleep Disorders Centre of the University of Heidelberg, men and women were exposed to either the smell of flowers or hydrogen sulphide, or to no smell at all. Results show that the emotional content of subsequent dreams was linked to the smell. Those who had the pleasant smell had significantly more pleasant dreams than those who had no smell and the people exposed to the sulphur smell had the most negative dreams. Researchers are now looking at whether pleasant smells could reduce the risk of nightmares.
How smell affects insomnia and stress
Lavender, vanilla, coffee and roses can each help. Clinical trials have shown that the smell of lavender can help in insomnia, anxiety, stress, and post-operative pain, according to a report from Maryland University. "There is now scientific evidence to suggest that aromatherapy with lavender may slow the activity of the nervous system, improve sleep quality, promote relaxation, and lift mood in people suffering from sleep disorders," say the researchers.
The smell of coffee can also lead to a calming effect, according to researchers at The University of California. A study at Tubingen University in Germany shows that vanilla fragrance has a calming effect, while a Thailand study showed the smell from roses reduces both breathing rate and blood pressure.
How smell affects blood sugar levels
In a study carried out at Cardiff University, insulin was injected into healthy men once a day for four days and their blood glucose levels fell. Each time they were injected, they were exposed to a smell, but on the fifth day the men were just given the smell... and their blood glucose still fell.
How smell affects concentration
Peppermint, strawberry and lavender have all been found to help. Spraying the scent of lavender during factory tea breaks in Japan has been shown to improve post-break production. Athletes who sniffed peppermint ran faster and had better concentration than those who had no smell, while children performed better at tests when exposed to the aroma of fresh strawberries.
How smell affects memory
Smells are very powerful triggers of specific memories, and are used in therapy to help recover lost memories. Research at Toronto University shows that memories triggered by smells tend to be clearer, more intense and more emotional. One theory is that this is because the part of the brain that processes smell has direct links with parts that are involved in emotion and memory.
How smell affects love
Research at Chicago University has shown that women are able to smell genetic differences. Researchers say we tend to prefer smells of people with different genetic material involved in immunity. And that, they say, is because mating with such an individual would give offspring a stronger immune system.