I always knew it. But for the first time it has been scientifically measured. A new study has shown that unpleasant smells attack the immune system and that good smells lift it.
The research was part of the recent Arise pleasure and immunity conference. Arise - the Associates for Research into the Science of Enjoyment - is kind of the Martyn "Good News" Lewis of the science world. They are a group of scientists who look at how good things can keep us healthy, to balance the traditional research route of problem solving.
The smell test was done by Dr Angela Clow, senior lecturer in psychophysiology at the University of Westminster. In the test three groups of people were exposed to the smell of rotten meat, melted chocolate and water - representing (unsurprisingly) unpleasant, pleasant and neutral smells.
They were blindfolded, exposed to the smells and asked how they felt after each exposure, and their saliva was measured for the concentration and secretion rate of secretory Immunoglobulin-A (sIgA).
The most interesting result was the difference between men and women's responses. It may explain why men are such insensitive malodorous beasts and women are such whining wimps. Women's reporting of how awful the meat was and how calming the chocolate was far more extreme. The men apparently didn't notice the whiffs so much either way (which accounts for the unequal division of laundry labour). However the male immune response was actually stronger than the women's - positive for the chocolate, negative for the meat. They were suffering in silence.
Why should smell affect our immune system? Probably it's evolutionary. "Odour is processed in the same evolutionary ancient part of the brain as the emotions," says Dr Clowe.
The obvious inference is that we should take a lot more note of the aromas surrounding us. Maybe we will soon sue fast-food restaurants, not because their coffee is too hot but because the greasy smell that guffs out of the air vents gives us bad vibes. What the study does not show is whether the effects are momentary or longer lasting, but it does suggest that it is a good thing to fill your house and office with pleasant smells.
The study also did not measure whether smell affects the body's second line of defence, the internal circulatory immune system which would be more important for the development of smell therapies. "There is a `common sense' idea that smells can be uplifting," says Andrew Vickers, director of research at the Research Council for Complementary Medicine. "But in the case of aromatherapy, the success is so far largely anecdotal. A smell alone is not an effective cure for depression, for example."
Another important point when deciding which smells will enhance your immune system may be personal association. Says Andrew Vickers: "There was an experiment where people were given a stressful intelligence test impregnated with a scent that was detectable, but not so strong that they would consciously register it. Afterwards, when the people encountered the same smell, they felt stressed." So before you fill your office with scented candles, know your own smells. Lavender is not oh-so-relaxing if, like me, you associate it with a recently deceased grandmother.
These are early days in smell and immune response research, but personally I can't wait for the time when people with too much perfume on are forced to wear government health warnings.