At the start of Korean-Canadian director Celine Song’s film Materialists (2025), a Neanderthal couple rubs noses in an act that seems an embodiment of love itself. Nose-to-nose contact, popularly known as the Eskimo kiss, has been documented in many mammals’ behavior. A recent study confirms that, beyond being a mere show of affection, such nose bumps can be an important element in social communication, even for antisocial species.
Biologist Sophie Lund Rasmussen, author of the study recently published by the journal Evolution and Human Behaviour, says her interest in the subject sprang from the kind of mouth-to-mouth kisses that take place between humans, chimpanzees, and bonobos. Along with her husband, Lund published an article entitled “The ancient history of kissing” in Science, which focused on whether humans have always exchanged kisses. “It was really fun to research, it’s not a typical subject in science,” recalls the biologist, who is associated with the University of Oxford and Denmark’s Museum of Natural History. While observing animals, she reflected on how even if they don’t kiss like humans, many touch noses. “I think that the majority of us have witnessed this at some point,” she says. It seemed logical that there would be scientific literature exploring the phenomenon, but she was unable to find any. The behavior is mentioned briefly, however, in studies focused on other subjects.
Among humans, kissing is associated with sexual arousal, a couple’s bond, intimacy, and the exchange of chemical information. Lund asked herself if something similar could be taking place between animals. She decided to collect examples of different species kissing.
In the resulting text, the researcher holds that nose-to-nose contact can fulfill very different functions, varying by species and context. Among social animals, the gesture appears to have more uses than among solitary creatures. Information exchanged via the gesture can include reproductive status, health, belonging to a group, and even the strength of a potential rival. “If chemical signals indicate that the other individual is very strong and healthy, they may decide not to fight,” Lund says.
The biologist believes that this type of contact among social species helps to maintain group cohesion and can be the difference between life and death. A brief nose brush can avoid conflict, reinforce trust, and facilitate cooperation.
Greetings, links, power
Among bats, a social species, nose-to-nose contact functions as a greeting and reinforces ties within a colony, Lund says. Some studies suggest that the act helps to distinguish individuals who belong to a group from those who do not. But generally speaking, the author admits, science has yet to examine which specific chemical substances are exchanged. “That would be truly interesting to study,” she says.
Kissing is observed among beavers between mates, parents, and offspring and siblings, which suggests that it functions as a way of recognizing others and as a sign of familial cohesion. But among pigs, it works differently, with the gesture translating to physical well-being and reproductive success. Studies cited in Lund’s review prove that piglets that receive more nasal contact grow faster and have better chances of surviving.
One extreme case is that of the naked mole rat, which is among the few eusocial (the highest level of sociality) mammals. In their subterranean communities, the queen utilizes nose-to-nose shoves to maintain her dominance and repress reproduction among subordinates, says the expert.
Sensory overload
Among the less social, the meaning of nose-to-nose contact changes radically. The European hedgehog, a solitary and nocturnal animal, is one of the most compelling examples. During field observations, Lund documented unexpected interactions in which two hedgehogs wound up accidentally touching noses while sniffing each other. (She observed the same behavior between cats.) After that contact, both animals would become immobile for several seconds, their pupils dilated, apparently disassociating from their surroundings. Such chemical interactions seemed so intense that they forced the animal to process information before it could react. “It’s like a sensory overload,” says the researcher.
For Carmen Agustín Pavón, a Spanish neurobiology researcher, the act of two animals approaching and smelling each other face-to-face is no trivial gesture. On the contrary, such contact activates cerebral mechanisms involved in the regulation of mammals’ social and emotional behavior. “The majority of mammals do not have a single olfactory system, but two,” she says. On one hand, they have a primary olfactory system, which is tasked with detecting volatile odors in the air, similar to that of humans. On the other hand, there is the vomeronasal system, which specializes in detecting pheromones, less volatile chemicals that require close contact to be detected.
The cerebral structure shared by mammals, reptiles, and other vertebrates is closely tied to their social and emotional behavior, says Agustín Pavón, who carried out her postdoctoral research at the University of Cambridge. “The olfactory signal in just two neuronal connections reaches to the emotional and social center of the brain,” she says.
In contrast to humans and other primates, who largely depend on sight, the majority of mammals are primarily guided by smell. “They don’t focus on what they see, but rather the chemical signals they receive,” explains the researcher, who is from Valencia, Spain. And among species like mice, hedgehogs, and naked mole rats, smell is the primary method for interpreting the social environment.
Similar cultural practices
To Lund, it’s not unthinkable that the human kiss constitutes a cultural transformation of a much older sensorial behavior. Face-to-face contact appears in an array of human cultures, from nose-rubbing in Hawaii and New Zealand to similar practices among the Inuit of Greenland. “The fact that this behavior continues to exist suggests that it fulfills an important function,” she says. If not, Lund believes it would have long ago disappeared.
Lund hopes that other researchers will dig deeper into this behavior, analyze it experimentally, and discover what is really being transmitted in those brief, nose-to-nose encounters. “The world needs good stories right now,” she says.
Sign up for our weekly newsletter to get more English-language news coverage from EL PAÍS USA Edition