Friendship is closely tied to both mental and physical health. Strong social connections are associated with lower stress, improved emotional well-being, and longer life expectancy. Large population studies indicate that people with stronger social networks tend to experience lower rates of chronic disease and mortality(1,2).
From an evolutionary perspective, friendships also had practical value.
For our ancestors, trusted allies meant cooperation, protection, and shared resources. Relationships within small groups improved survival and reproductive success(3).
Yet when we meet someone new, we often form impressions very quickly. Within minutes, sometimes seconds, we begin to sense whether a relationship might develop.
One influence on that judgment may be something we rarely think about consciously: how a person smells.
When encountering a new person, the brain quickly gathers clues to answer a basic question: Is this someone I can trust?
Because these judgments must occur rapidly, the brain relies on cognitive shortcuts known as heuristics. A heuristic is a mental rule of thumb that allows people to make decisions quickly using limited information(4).
Most people assume these snap judgments depend primarily on visual cues, such as facial expressions, posture, or eye contact. Visual information plays a powerful role in forming first impressions and predicting social preferences(5).
But another sense contributes quietly in the background, which is smell.
Each person produces a unique pattern of natural body odors. Scientists sometimes refer to this as a body odor signature, influenced by genetics, metabolism, diet, and the microorganisms that live on the skin(6).
In everyday life, however, we rarely encounter someone’s completely natural scent. Instead, what we perceive is a more complex blend that researchers call 'diplomatic odor.'
Together, these elements create the scent that accompanies someone in social settings. Even if we are not consciously aware of it, this scent becomes part of the sensory information the brain uses when evaluating others.
Among the senses, smell has a particularly strong connection to the brain regions involved in emotion and memory, including the amygdala and hippocampus. These areas help determine how experiences feel and how they are stored in memory(7).
This neurological connection helps explain a common experience: a familiar scent can suddenly bring back vivid memories or emotions. The smell of sunscreen may evoke childhood summers, while a particular laundry detergent might remind someone of home.
Remarkably, the brain can form these associations after only a few exposures.
Researchers believe similar learning occurs with the scents associated with other people.
Over time, the brain begins to associate a person’s scent with the emotional tone of interactions shared with them.
If encounters with someone are warm and enjoyable, the scent linked to that person may gradually take on a positive emotional meaning. If interactions are tense or unpleasant, the opposite can occur.
This process reflects associative learning, in which the brain connects a sensory cue with an emotional experience.
Many everyday experiences reflect this mechanism. People often find comfort in the scent of a partner’s clothing when they are apart. In other cases, a familiar smell may trigger discomfort because it is tied to an unpleasant memory.
In effect, the brain learns to connect a person’s scent with the emotional history of the relationship(7).
For decades, scientists studying human scent focused largely on romantic attraction and mate selection. Research has shown that body odor can influence perceptions of attractiveness and compatibility(6).
Yet most human interactions are not romantic. Daily life is filled with platonic relationships among friends, classmates, and coworkers. Despite their importance, the role of scent in friendship formation has received far less scientific attention.
To investigate these questions, researchers designed an experiment modeled after speed dating, sometimes called speed friending.
Female participants met several other women in a series of short conversations lasting four minutes each. After every interaction, participants rated the other person’s friendship potential, meaning how likely they felt a friendship could develop. The study also included two separate evaluations.
Before and after the event, participants smelled T-shirts worn by the other women during their normal daily routines. These shirts carried the individuals’ diplomatic scent, including natural body odor along with typical fragrances and hygiene products.
Participants rated how appealing each scent seemed and how much friendship potential they associated with the person based solely on smell.
Participants also viewed brief portrait photographs of the same individuals. Each photo appeared for only 100 milliseconds, roughly the duration of a blink, allowing for a rapid visual impression.
Figure: Schematic Representation of Study Procedures and Key Measures. The study design consisted of four parts. (A) An in-person pre-interaction session wherein participants provided their informed consent, had their photographs taken, and were given materials for the odor collection phase, (B) an online pre-event session wherein participants completed self-report measures and a portrait judgment task (i.e., based on a 100-ms exposure to targets’ portrait), (C) a diplomatic odor collection phase wherein participants wore a t-shirt as they took part in their daily activities, and (D) an in-person speed-friending session that included a pre-interaction rating of t-shirts worn by those in the session, the live speed-friending session, and post-interaction rating of the same t-shirts. (Adapted from Gaby, Gunaydin & Zayas, 2025)
Both visual impressions and scent-based impressions helped predict how participants felt after meeting someone in person.
In other words, a person’s scent provided meaningful information that contributed to social impressions alongside visual cues.
Smell was not merely background sensory noise. It played a measurable role in shaping first impressions about friendship potential.
The study revealed another intriguing effect. After participants had conversations with someone, their ratings of that person’s scent shifted.
Positive interactions tended to make the scent seem more pleasant, while negative interactions made the same scent seem less appealing.
This finding suggests that the brain updates scent associations based on social experience. As relationships develop, the emotional meaning attached to a person’s scent may strengthen or change. Over time, this process may help reinforce social bonds.
The researchers also examined how much agreement existed across participants about who seemed like a good potential friend.
A large portion of the variation came from individual preferences rather than shared consensus. Nearly half of the differences in friendship ratings reflected personal taste.
Two people can meet the same individual and form very different impressions.
Such variation is consistent with many other social judgments, including perceptions of attractiveness or personality(5).
The results also suggest that smell and vision contribute different types of information when we evaluate someone.
Visual cues convey details about facial expressions, age, health, and emotional state. Scent may carry subtler signals related to biological traits, hygiene habits, and environmental influences.
Rather than duplicating the same information, these senses appear to complement one another, allowing the brain to build a richer picture of the person in front of us(6).
Many laboratory studies of human scent rely on controlled conditions in which participants smell isolated body odor samples. Real social interactions are far more complex.
This research suggests that even within this rich sensory environment, scent still contributes to how we evaluate others.
When meeting someone new, the brain rapidly gathers information from several senses to form an impression.
Smell is part of that process, even if we rarely notice it consciously.
Over time, the brain links a person’s scent with the emotional tone of our interactions. Positive experiences may make that scent feel familiar and pleasant, while negative encounters can produce the opposite effect.
In this way, scent becomes part of the subtle sensory background that shapes human relationships. Our noses may not consciously choose our friends. But the evidence suggests they quietly contribute to the decision.
If you've got friends, then there's a good chance your nose played a role in deciding that. But smell is just the beginning, because it takes a lot to nurture friendships that last a lifetime. Sometimes it just takes checking in with someone to keep that spark alive.
If there's someone in your life you've thought about reaching out too but haven't talked to in a while and want to know a powerful question that has been shown to improve someone's mood, click here.
References:
