Your skin is teeming with bacteria. There are billions of them, living on the dry parched landscapes of your forearms, and the wet, humid forests of your nose. On your feet alone, every square centimetre has around half a million bacteria. These microbes are more than just passengers, hitching a ride on your bodies. They also affect how you smell.
Skin bacteria are our own natural perfumers. They convert chemicals on our skin into those that can easily rise into the air, and different species produce different scents. Without these microbes, we wouldn’t be able to smell each other’s sweat at all. But we’re not the only ones who can sniff these bacterial chemicals. Mosquitoes can too. Niels Verhulst from Wageningen University and Research Centre has just found that the bacteria on our skin can affect our odds of being bitten by a malarial mosquito.
The English language is full of metaphors linking moral purity to both physical cleanliness and brightness. We speak of “clean consciences”, “pure thoughts” and “dirty thieves”. We’re suspicious of “shady behaviour” and we use light and darkness to symbolise good and evil. But there is more to these metaphors than we might imagine. The mere scent of a clean-smelling room can take people down a virtuous road, compelling them to choose generosity over greed and charity over apathy. Meanwhile, the darkness of a dimmed room or a pair of sunglasses can compel people towards selfishness and cheating.
These new results are the latest from psychologist Chen-Bo Zhong. Back in 2006, he showed that people who brought back memories of past wrong-doings were more likely to think of words related to cleaning, or to physically crave cleaning products. He called this the “Lady Macbeth effect”. Subsequently, another group found that it works the other way too. People judge moral transgressions more leniently if they had previously washed their hands or if they had been primed with words related to cleanliness, like ‘pure’ or ‘immaculate’.
Now, Zhong, together with Katie Liljenquist and Adam Galinsky, have expanded on these studies by showing that clean smells can make people behave more virtuously. They ushered 28 volunteers into a room that was either unscented or that had been lightly sprayed with a citrus air freshener. In either case, they had to play a trust game, where a “sender” has a pot of money and chooses how much they want to invest with a “receiver”. The investment is tripled and the receiver decides how much to give back.
The volunteers were all told that they had been randomly chosen as receivers. Their anonymous partner had invested their entire $4 pot with them, which had been tripled to $12. Their job was to decide how much to give back. On average, they returned a measly $2.81in the unscented rooms but a more equitable $5.33 in the scented ones. The single spray of citrus nearly doubled their tendency to reciprocate.
In a second experiment, the trio again ushered 99 students into either a scented or unscented room. They were given a pack of miscellaneous tasks, including a flyer requesting volunteers for a charity called Habitat for Humanity. Those in the citrus-scented rooms were more likely to be interested in volunteering, and almost four times more willing to donate money to the cause.
Pregnant women are generally advised to avoid drinking alcohol and for good reason – exposing an unborn baby to alcohol can lead to a range of physical and mental problems from hyperactivity and learning problems to stunted growth, abnormal development of the head, and mental retardation.
But alcohol also has much subtler effects on a foetus. Some scientists have suggested that people who get their first taste of alcohol through their mother’s placenta are more likely to develop a taste for it in later life. This sleeper effect is a long-lasting one – exposure to alcohol in the womb has been linked to a higher risk of alcohol abuse at the much later age of 21. In this way, mums could be inadvertently passing down a liking for booze to their children as a pre-birthday present.
Now, Steven Youngentob from SUNY Upstate Medical University and Jon Glendinning from Columbia University have found out why this happens. By looking at boozing rats, they have found that those first foetal sips of alcohol make the demon drink both taste and smell better.
The duo raised several pregnant rats on diets of either chow, liquids or liquids that had been spiked with alcohol. The third group eventually had a blood alcohol concentration of about 0.15%, a level that would cause a typical human to slur, stagger or become moody.
When the females eventually gave birth, month-old pups born to boozy mothers were more likely to lick an alcohol-coated feeding tube than those whose mothers were tee-total. These rats had been born with more of a taste for booze.
Bad experiences can be powerful learning aids for our sense of smell. A new study reveals that electric shocks can make people more sensitive to the differences between very similar chemicals that previously smelled identical.
Every day, thousands of different molecules waft past our nose. Many of these are uncannily similar and some are more important to others. Wen Li from Northwestern University wanted to see how people learn to distinguish the critical smells from the unimportant ones.
Smell the difference
Working in the lab of smell guru, Jay Gottfried, Li attempted to train 12 volunteers to smell the difference between a pair of enantiomers – molecules that are mirror-images of each other but are otherwise identical. The two chemicals were versions of 2-butanol and both had a grassy tang. At first, Li asked volunteers to sniff the odd one out between three bottles, two that contained one molecule and a third that contained its mirror-image. On average they scored 33%, no more accurate than complete guesswork.
Their scores more than doubled when Li gave the volunteers an electric shock whenever they were exposed to one enantiomer, but not the other. Li didn’t provide any shocking impetus for a second pair of mirror-image molecules and accordingly, this control pair remained indistinguishable throughout the experiment.