Smell is one of the most ancient human faculties — it has also been the least understood by science until recently. Biologists first uncovered the inner workings of chemical sensors in our noses, otherwise known as olfactory receptors, in the early 1990s, a finding that lead to a Nobel Prize.
But the story doesn’t end there. Over the last decade, scientists have discovered that smell receptors are not only found in the nose, but also throughout the body — in the brain, colon, heart, liver, kidneys, spine, prostate and even sperm — and play a crucial role in a range of physiological functions. And now, a team of researchers at Ruhr University Bochum in Germany have confirmed even our skin is covered with these receptors.
“More than 15 of the olfactory receptors that exist in the nose are also found in human skin cells,” said lead researcher, Dr. Hanns Hatt. What’s more, exposing the skin receptors to specific odors triggers a cascade of reactions that prompt healing of injured tissue.
An Unconventional Way of Using Scent to Heal
The researchers in Germany are enthusiastic about our sense of smell — although, not via the nose, but the skin. Writes Bob Roeher in New Scientist:
“They found that Sandalore—a synthetic sandalwood oil used in aromatherapy, perfumes and skin care products—bound to an olfactory receptor in skin called OR2AT4. Rather than sending a message to the brain, as nose receptors do, the receptor triggered cells to divide and migrate, important processes in repairing damaged skin.
Cell proliferation increased by 32 per cent and cell migration by nearly half when keratinocytes [skin cells] in a test tube and in culture were mixed for five days with Sandalore.”
It may seem bizarre to have scent receptors beyond the nose, but Dr. Hatt and other researchers point out that odor receptors are some of the most evolutionarily ancient chemical sensors in the body, able to detect a profusion of compounds, not simply those floating in the air. It’s also not clear whether olfactory receptors in the nose were the first to develop in our evolutionary past.
“They’re called olfactory receptors because we found them in the nose first,” said Yehuda Ben-Shahar, a biologist at Washington University in St. Louis who published a paper in 2014 year on olfactory receptors in the human lung, which he found act as a safety switch against poisonous compounds by causing the airways to constrict when we inhale noxious substances. “It’s an open question,” he said, “as to which evolved first.” [source]
The receptors operate as a lock-and-key system, where an odor molecule acts like a key to the receptors lock. Only specific molecules will plug into specific receptors. When the right molecule “clicks” with the matching receptor, it activates a complex set of biochemical reactions.
“If you think of olfactory receptors as specialized chemical detectors, instead of as receptors in your nose that detect smell, then it makes a lot of sense for them to be in other places,” notes Jennifer Pluznick, an assistant professor of physiology at Johns Hopkins University who discovered in 2009 that smell receptors in the kidneys of mice help regulate metabolic function and control blood pressure.
This isn’t the first time science has discovered smell receptors in a strange place. In 2003, Dr. Hatt and his colleagues found that olfactory receptors within the testes function like a biochemical guidance system, which allows the sperm to locate an unfertilized egg. And in 2009, the team also reported that subjecting olfactory receptors in the human prostate to beta-ionone, a scent compound found in violets and roses, slowed the spread of prostate cancer cells by way of turning off misbehaving genes.
“I’ve been arguing for the importance of these receptors for years,” said Dr. Hatt, who calls himself an ambassador of smell, and whose favorite aromas are basil, thyme and rosemary. “It was a hard fight.” [source]
Grace Pavlath, a biologist at Emory University, is also intrigued by unusually placed olfactory receptors. While studying the receptors in skeletal muscles, she discovered that by soaking them in Lyral — a synthetic fragrance similar to lily of the valley — muscle tissue regeneration was increased. When she blocked the receptors, muscular regeneration was inhibited, leading her to believe that smell receptors are an integral part of the biochemical signaling system, which prompts stem cells to morph into muscle cells and heal injured tissue.
These findings hold promise for the development of pharmaceuticals and cosmetics, such as a smell-based drug that helps to regenerate muscle tissue after an injury, or a topical cream that would accelerate wound healing. The researchers are hopeful that new and innovative ways to utilize olfactory receptors is just around the corner.