How much does smell shape how people see you?

When you meet someone for the first time, what makes you think, "This person seems nice"?

Most people would say their face, their clothes, the way they talk. But follow the research and another, often overlooked, cue appears: smell. And we use it without being aware of it.

In this article, I sort through research in psychology and chemistry on how smell affects the impressions we form of people. I'll also check some popular claims that have spread too far, like "pheromones."

1. Smell changes likes and dislikes outside awareness

First, the most surprising finding.

In one experiment, participants were shown photos of faces with neutral expressions while being exposed to smells too faint to consciously detect. There were two kinds of smell, pleasant and unpleasant. When they then rated how likable the faces were, faces paired with the pleasant smell tended to be rated more favorably.^[1]

Part of the impression that someone "just seems nice" may be created by smells that never reach awareness.

2. Smell is a clue to emotion and personality

It isn't only likes and dislikes that smell conveys.

In one experiment, other people smelled sweat collected while donors felt fear and while they felt disgust. In the receivers, fear-related chemical signals produced facial expressions and sensory-acquisition responses related to fear, and disgust-related ones produced responses related to disgust.^[2] The result suggests that information about emotion may have been passed on without words or sight.

There are also reports about personality. In a study where people judged others' personalities from body odor, judgments for some traits matched the odor donors' self-rated personality scores to some degree.^[3] But that's at the level of "for some traits, to some degree." We can't go as far as saying smell reveals personality.

3. Smell and attraction: preferences do exist

Some research shows that scent preferences play a part in judging attractiveness.

• Women near ovulation have been reported to prefer the scent of men with more symmetrical bodies.^[4] But results like this aren't always consistent in replications.
• In an experiment manipulating men's scent, the scent changed the men's own confidence and self-rating, and women watching videos of those men rated their attractiveness differently. With photos alone, no difference was found.^[5]

4. How true are "pheromones" and "scent compatibility"?

Now for topics that need checking.

You often see phrases like "attract the opposite sex with pheromones" in ads and articles. But a strong argument from researchers is that no human pheromone has been established so far.^[6]

There's also the claim that "you can tell genetic compatibility by smell." It started from reports that people prefer the smell of partners whose immune-related genes (MHC) differ from their own.^[7] But a review of later research found that results were inconsistent from study to study.^[8]

So it's appropriate to take this area no further than "such a tendency has been reported." Be careful with definitive claims.

5. Age-related body odor is real: research from Japan

In Japan there's a common word, kareishū, for the body odor that comes with aging.

A research group at Shiseido detected a compound called 2-nonenal in the body odor of people over 40, and showed it tends to increase with age.^[9] In other words, there's chemical support for changes in body odor with aging.

But care is needed here. Identifying a compound is a separate question from whether people find the smell unpleasant. How people perceive smells varies between individuals and is shaped by culture and experience. Labeling it a "bad smell" goes beyond what the research shows.

6. Smells stick in memory

One reason impressions from smell last is their link to memory.

Autobiographical memories triggered by smells tended to be experienced as more emotional and evocative than memories triggered by visual or auditory cues.^[10] When someone's smell brings back the very scene where you met, this kind of background is probably at work.