Why do people cuddle? According to a slew of media reports, that answer lies in oxytocin, dubbed either the “cuddle chemical” or the “love hormone.” English pharmacologist and neurophysiologist Sir Henry Hallett Dale was the first to isolate oxytocin from pituitary extract in 1921, eventually receiving the 1936 Nobel Prize in medicine and physiology for the discovery. Dale’s work on oxytocin was prompted by his interest in the ergot fungus, extracts of which had a long history of use for stimulating the contractions of the pregnant uterus. The question was why.
In 1909, Dale had prepared an extract from the posterior lobe of the pituitary and showed that it caused contractions of the uterus when injected into a pregnant cat. As a result, pituitary extract replaced ergot preparations as the prime method to induce labour. Dale hypothesized that the reason ergot stimulated contractions was because it contained some component that resembled a substance that women in labour produced naturally. But what was that component? Dale wasn’t successful in isolating the active ingredient from ergot, but eventually did manage to isolate oxytocin from pituitary glands, deriving the name of the newly discovered substance from the Greek for “quick birth.” Ergometrine, the active ingredient in ergot, was finally isolated and identified in 1935 by one of Dale’s former colleagues, Harold Ward Dudley.
But how did the connection to behaviour come about? That first emerged from an investigation of the love life of the prairie vole. These mammals are unusual in that they are monogamous. What makes them so? It seems their love is rooted in the release of oxytocin. When a couple engages in sex for the first time, oxytocin is released, somehow formalizing the union. From then on, the voles only have eyes for each other. Blocking the release of oxytocin with an oxytocin antagonist, which basically is a modified form of oxytocin, results in one-night stands. Should prairie voles be injected with oxytocin, they will search for a partner, and even if they are prevented from having sex, will continue to stay with the chosen partner.
On the other hand, a close relative, the “montane vole,” is immune to the effects of oxytocin, apparently having no receptors for the chemical. Other mammals do have receptors, even though they may not be monogamous. Sheep, for example, reject their young if treated with oxytocin antagonists, and female rats injected with oxytocin will nurture another’s pups as if they were their own. In rats, injection of oxytocin into the cerebrospinal fluid causes spontaneous erections, and there is some evidence that the hormone also plays a role in the female’s willingness to bend to the male’s desires. Some marketers of oxytocin highlight this effect and insinuate, without any evidence, that the chemical might have such uplifting effects in humans as well.
Humans obviously do have receptors for oxytocin, otherwise, the chemical would have no biological activity. Aside from uterine contractions, the chemical appears to play a role in stimulating bonding between mother and child. Studies have also shown that humans who sniff oxytocin via a nasal spray become more trusting. In one interesting study, volunteers treated with oxytocin invested more money in a questionable business venture than those treated with placebo even when they were told that there was no guarantee that the trustee was trustworthy.
Other studies have linked exposure to oxytocin with reduced social anxiety, but there have also been some disturbing observations with existing biases being strengthened when oxytocin was inhaled. Because of publicity given to preliminary data about improved social connections, it comes as no surprise that oxytocin nasal spray is being promoted on the web as a treatment for autism. There is some evidence of minor benefits, but long-term risks are unknown. As far as cuddling or falling in love, or some sort of aphrodisiac effect, unfortunately, there’s no evidence. Experiments with human couples sniffing oxytocin have not shown any increased tendency to fall in love or even to cuddle. Better to rely on personality than a nasal spray.