Why Is Oxytocin Called the 'Cuddle Hormone'?

From the delivery room to the nickname

Oxytocin wasn’t discovered in a hug but in a uterus. In the early twentieth century, British physiologist Henry Dale observed that an extract of the pituitary gland triggered uterine contractions. The name comes from Greek and means “swift birth.” In 1953, Vincent du Vigneaud managed to synthesize it, the first peptide hormone made in a laboratory, and received the 1955 Nobel Prize in Chemistry for it.

For decades it was the hormone of childbirth and breastfeeding. The leap into emotional life came in the early nineties with a rodent: the prairie vole, which forms stable pairs, unlike its close relatives, the montane voles. Thomas Insel and Lawrence Shapiro showed in 1992 that the two species distribute oxytocin receptors in the brain differently, and in 1994 the team of Jessie Williams, with Insel and Sue Carter, saw that administering it into the brains of female voles made them more likely to prefer a particular male.

From there to headlines about the “love hormone” and the “cuddle hormone” was a short step. The interesting question is how much of that holds up in people.

What the hugging studies do show

The study most often cited for the nickname is by Kathleen Light, Karen Grewen and Janet Amico, published in Biological Psychology in 2005. They measured blood oxytocin and blood pressure in 59 women before and after a period of warm contact with their partner that ended in a hug.

Women who said they received hugs more often had higher resting oxytocin levels and lower blood pressure and heart rate. Oxytocin partly explained that relationship. It’s a real and modest finding: a small sample, only premenopausal women with partners, and a correlational design that doesn’t tell us what causes what.

That limit matters more than it seems, because measuring oxytocin in blood is difficult. Michael McCullough, Patricia Churchland and Armando Mendez warned in 2013 that many of the methods used in these studies produced unreliable figures, and that part of the literature on oxytocin and behavior rested on those measurements.

The trust experiment and its replication

In 2005, Michael Kosfeld, Ernst Fehr and their team published an experiment in Nature that went around the world: people who received oxytocin through the nose transferred more money to a stranger in an economic trust game. The title left no doubt: “Oxytocin increases trust in humans.”

A decade later, Gideon Nave, Colin Camerer and McCullough himself reviewed the whole body of research in Perspectives on Psychological Science (2015). Their conclusion was that the most promising finding hadn’t replicated well, that blood measurements were flawed, and that large genetic studies found no consistent associations. The accumulated evidence didn’t support saying that oxytocin reliably increases trust.

Fehr himself later took part in a registered replication, with the protocol approved before any data were collected, published in Nature Human Behaviour in 2020. With more than 300 participants, it found no effect under the conditions of the original experiment. In 2026, a team from Maastricht replicated the study with 211 people, pooled their data with the 2020 data, and concluded that, if the effect exists, it’s too small for most laboratories to detect.

The debate isn’t closed. That same year, another preregistered study with 359 men with low baseline trust found that oxytocin increased their transfers by around 15%. The most cautious reading today is that, if oxytocin influences trust, it does so in specific people and contexts, not as a universal serum.

The less friendly side: looking after our own

There’s another reason to be wary of the nickname. In 2010, Carsten De Dreu and his team published three experiments in Science with men who received oxytocin or a placebo and made economic decisions affecting their own group and a rival group.

Oxytocin increased what they called the “tend and defend” pattern: more sacrifice for one’s own group and, under some conditions, more willingness to defend against the rival group. A year later, the same team reported in PNAS that oxytocin promoted ethnocentrism: stronger preferences for one’s own group over others.

That’s why many researchers no longer speak of a hormone of kindness, but of a hormone that makes social signals more salient. It makes the people close to us matter more, for better and, sometimes, at the expense of those left outside.

Why the nickname still makes sense (with caveats)

None of this means oxytocin has nothing to do with bonding. In mammals it plays a role in childbirth, breastfeeding and caring for the young, and in species like the prairie vole it’s involved in pair formation. In people, affectionate touch is associated with some physiological markers of calm.

What doesn’t hold up is the simple version: that a hug releases a dose of oxytocin that makes us trusting and kind. The hormone is part of complex systems, acts differently depending on context and person, and is hard to measure.

For attachment psychology, this fits well. What protects us isn’t an isolated molecule but the repeated experience that someone is available when we need them. Oxytocin would be one of the biological pieces of that process, not its full explanation.

Marian Rojas Estapé’s popular-science reading

Spanish psychiatrist Marian Rojas Estapé devotes the first chapter of Encuentra tu persona vitamina (2021) to oxytocin, and her book has popularized the nickname in Spanish. She presents oxytocin as the counterpoint to cortisol, which she calls “an old acquaintance,” and describes contemporary life as “inflammatory” because of a low but sustained activation of stress.

Two ideas from her chapter fit the research:

• Her warning against “hormonal determinism”: hormones influence mood and behavior, but they don’t dictate them mechanically or cancel out biography, context or will.
• Her clinical practice: she says that in the first interview she always asks about the patient’s relationships (partner, family, friends, work), because distress often originates in that sphere. That’s her experience, not a measured finding, but it matches what research on social support has been describing for decades.

To argue that human beings need connection, she contrasts Aristotle’s “social being by nature” with the phrase Thomas Hobbes popularized, “man is a wolf to man,” which comes from a comedy by Plautus. Her thesis is that competition exists, but coexists with a need for belonging that the pandemic and its lockdowns made visible.

It’s a popular-science book, and it’s best read as such: when it simplifies oxytocin as the “calm hormone,” it stays with the friendliest part of a more complex story.

What we still don’t know

• Whether nasal oxytocin reaches the brain in sufficient quantity, and by what route. Gareth Leng and Mike Ludwig raised this in 2016 as one of the field’s big unknowns, and it helps explain the inconsistency of the results.
• Whether effects in people depend on their starting profile, as the studies with low-trust individuals suggest.
• How closely oxytocin’s role in human bonding resembles the role it plays in monogamous rodents.

If you’re curious about how the patterns of closeness this hormone accompanies take shape, Bowlby and Ainsworth’s attachment theory explains them from childhood onward. We cover it in secure attachment and anxious attachment, and you can explore your own style with our attachment style test.

Sources

• Insel, T. R., & Shapiro, L. E. (1992). Oxytocin receptor distribution reflects social organization in monogamous and polygamous voles. Proceedings of the National Academy of Sciences, 89(13), 5981-5985.
• Williams, J. R., Insel, T. R., Harbaugh, C. R., & Carter, C. S. (1994). Oxytocin administered centrally facilitates formation of a partner preference in female prairie voles (Microtus ochrogaster). Journal of Neuroendocrinology, 6(3), 247-250.
• Light, K. C., Grewen, K. M., & Amico, J. A. (2005). More frequent partner hugs and higher oxytocin levels are linked to lower blood pressure and heart rate in premenopausal women. Biological Psychology, 69(1), 5-21. doi:10.1016/j.biopsycho.2004.11.002
• Kosfeld, M., Heinrichs, M., Zak, P. J., Fischbacher, U., & Fehr, E. (2005). Oxytocin increases trust in humans. Nature, 435(7042), 673-676. doi:10.1038/nature03701
• De Dreu, C. K. W., Greer, L. L., Handgraaf, M. J. J., Shalvi, S., Van Kleef, G. A., Baas, M., Ten Velden, F. S., Van Dijk, E., & Feith, S. W. W. (2010). The neuropeptide oxytocin regulates parochial altruism in intergroup conflict among humans. Science, 328(5984), 1408-1411. doi:10.1126/science.1189047
• De Dreu, C. K. W., Greer, L. L., Van Kleef, G. A., Shalvi, S., & Handgraaf, M. J. J. (2011). Oxytocin promotes human ethnocentrism. Proceedings of the National Academy of Sciences, 108(4), 1262-1266. doi:10.1073/pnas.1015316108
• McCullough, M. E., Churchland, P. S., & Mendez, A. J. (2013). Problems with measuring peripheral oxytocin: Can the data on oxytocin and human behavior be trusted? Neuroscience & Biobehavioral Reviews, 37(8), 1485-1492. doi:10.1016/j.neubiorev.2013.04.018
• Nave, G., Camerer, C., & McCullough, M. (2015). Does oxytocin increase trust in humans? A critical review of research. Perspectives on Psychological Science, 10(6), 772-789. doi:10.1177/1745691615600138
• Leng, G., & Ludwig, M. (2016). Intranasal oxytocin: Myths and delusions. Biological Psychiatry, 79(3), 243-250. doi:10.1016/j.biopsych.2015.05.003
• Declerck, C. H., Boone, C., Pauwels, L., Vogt, B., & Fehr, E. (2020). A registered replication study on oxytocin and trust. Nature Human Behaviour, 4(6), 646-655. doi:10.1038/s41562-020-0878-x
• Kroll, C. F., Schruers, K. R. J., Viechtbauer, W., Vingerhoets, C., Seidel, L., Riedl, A., & Hernaus, D. (2026). Absence of a meaningful effect of intranasal oxytocin on trusting behavior: A registered report with pooled equivalence testing. Cortex, 198, 208-233. doi:10.1016/j.cortex.2026.03.006
• Vogt, B., Bengart, P., Declerck, C., & Fehr, E. (2026). Oxytocin increases trust in men low in dispositional trust. Proceedings of the National Academy of Sciences, 123(32), e2602655123. doi:10.1073/pnas.2602655123
• Rojas Estapé, M. (2021). Encuentra tu persona vitamina. Espasa.