Oxytocin is colloquially known as the "love hormone" but that might not be the only thing that it's responsible for. Involved in the human stress response, sleep and social bonding, oxytocin plays an important role in far more than just romance, sex and parenthood. You could even say oxytocin, not love, makes the world go round.
"Oxytocin is produced in the hypothalamus, but released into the bloodstream from the nearby pituitary gland," said Dr. Deborah Lee, a sexual and reproductive health specialist and medical writer for Dr Fox Online Pharmacy in the U.K. "Electrical excitation of neurons within the hypothalamus provides the stimulus for oxytocin production and secretion," she told Live Science.
Like antennas picking up a signal, oxytocin receptors are found on cells throughout the body. As a result, it has several different effects.
1. Attachment and bonding
Oxytocin plays a large role in those heady moments of initial attraction and the building of romantic attachments. A 2012 study in the journal Psychoneuroendocrinology tested oxytocin levels in the blood plasma of 163 young adults, including 120 new lovers (60 couples), three months after the initiation of their romantic relationship, and 43 non-attached singles. The attached couples had significantly higher levels of oxytocin than the singles, and the couples who stayed together still had high levels of oxytocin six months later.
"Oxytocin levels are known to rise in the early stages of a relationship," Lee said. "Certain areas of the brain that are rich in oxytocin receptors become activated such as the olfactory system, limbic structures, hypothalamus, hippocampus and brainstem."
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2. Stress and pain relief
A 2021 study in the journal Stress found that oxytocin levels began to rise a week before cortisol levels did in college-aged women who were approaching final exam season. Both hormones remained elevated over the exam period, during which the women were under an increased amount of stress.
This oxytocin surge might work to enhance cognitive accuracy and help to buffer the negative effects of cortisol, Lee said.
"Scientists have suggested that oxytocin may play a role in stress by interfering with the sympathetic nervous system's fight fright and flight response — such that the person under threat can stand their ground as opposed to fighting or fleeing," she said.
Additionally, oxytocin has been shown to help people better tolerate pain, with a 2015 review in Current Pharmaceutical Design finding that the analgesic (pain relieving), anxiolytic (anxiety relieving), antidepressant and other central nervous system effects make oxytocin a valuable form of therapeutic pain relief.
3. Labor and breastfeeding
In its best understood role, oxytocin is released in large amounts during labor, intensifying the uterine contractions that open the cervix and allowing the baby to pass through the birth canal. Physicians have been using synthetic oxytocin, also known by its brand name Pitocin, to induce or augment labor since the early 1900s.
According to a 2021 review in Frontiers in Endocrinology, after birth, the hormone continues to stimulate uterine contractions that discourage hemorrhaging, and more is released when the nipples are stimulated during suckling, promoting the letdown of milk into the nipples.
"During labor, the pressure of the baby's head as it pushes against the cervix results in nerve impulses which stimulate the hypothalamus and pituitary to release oxytocin," Lee said. "A positive feedback loop is in place, such that the more oxytocin is released, the greater the strength and frequency of the uterine contractions, the more the cervix thins and dilates, and the more oxytocin is produced.
4. Sexual arousal
Human sexual arousal is an endocrinological mishmash, with oxytocin as one of the key players, alongside testosterone.
"The release of oxytocin is one of the main reasons we feel in the mood for sex," Lee said. "Lighttouch, eye contact and skin-to-skin contact all play their part, leading to higher levels of oxytocin."
The more positive and close a relationship is with a partner, the greater the oxytocin release, Lee said. "Oxytocin release happens simply by looking at the other person. Undoubtedly, oxytocin levels are vital for sexual arousal, intimacy and a satisfactory sexual response," she said.
In women, oxytocin plays a role in orgasm too, with a study in the journal Gynecological and Obstetric Investigation finding that women had significantly higher oxytocin serum levels less than a minute after orgasming.
In men, oxytocin increases during arousal and peaks at orgasm. One 2008 study in the Journal of Sexual Medicine even found that oxytocin could be used to treat anorgasmia (delayed orgasm or failure to orgasm) in men. The study found that supplementary oxytocin delivered as a nasal spray helped these men to ejaculate.
5. Social bonding
Oxytocin has been recognised as vital in humans for their social behavior, Lee said. "This knowledge originated in laboratory studies in rats," she said. "Rats are not interested in any offspring other than their own, but when given oxytocin, they suddenly became affectionate and displayed maternal behavior to pups from other females. Prairie voles bond with a mate for a lifetime and are the most monogamous species on the planet. But when their oxytocin receptors are blocked, this close bonding behavior is reversed."
Natural oxytocin levels may be lower in those with autism, a developmental disorder characterized by difficulties in communication and social relationships, according to a 2018 review in the journal Current Topics in Behavioral Neuroscience. In fact, a 2016 randomized controlled trial in the journal Molecular Psychiatry found that caregiver-rated social responsiveness was improved in autistic individuals who received supplementary oxytocin through a nasal spray.
6. Generosity
Generosity and altruism may seem like odd things to relate to a hormonal response, but research has shown that oxytocin can in fact impact how we empathize with others, according to the American Psychological Association.
A 2007 paper in PLoS One outlined this relationship between oxytocin and generosity, noting that humans are considerably generous towards each other, often helping complete strangers through donation of money, time and even blood, despite no direct benefits to themselves. In the study, participants were paired off, with one given a $10 endowment, and the other given nothing. Those given supplementary oxytocin gave 21% more of their $10 to the person with no money compared with those given a placebo and $10, indicating that having more oxytocin in our bodies may make us more generous.
