Ask what makes someone attractive and you are usually assuming that attractiveness is a property a person carries around, like height or eye color. Some people simply have more of it, and the rest of us can more or less agree on who.

The research says that is partly true and mostly misleading. There is real agreement about looks, but it is strongest exactly where it means least, among strangers, and it comes apart the better you know someone.

I am a writer, not a psychologist, so treat this as a careful reading of the research rather than expert testimony.

What strangers agree on

At first glance, people across very different cultures do converge on which faces they find attractive, and a few ingredients turn up again and again.

One is surprisingly dull: averageness. In a well-known 1990 study, Judith Langlois and Lori Roggman digitally blended many faces into composites and found that people rated the averaged faces as more attractive than almost all of the individual faces that went into them. A mathematically average face, it turns out, is unusually appealing, probably because it is easy for the brain to process. Symmetry helps too, though less than people tend to assume.

Familiarity is another quiet factor. We tend to like faces we have seen before, or that resemble faces we already know, an effect of simple exposure rather than merit. And on top of all this sits the halo effect, documented since the 1970s under the phrase “what is beautiful is good,” our habit of assuming attractive people are also kinder, smarter and more trustworthy, on no evidence at all.

So there is a real layer of consensus. It is also a shallow one, measured mostly on strangers judged in seconds.

The finding that changes the question

The more interesting result is what happens to that agreement over time, and here one study is worth dwelling on.

In 2015, the psychologists Lucy Hunt, Paul Eastwick and Eli Finkel studied 167 couples, looking at how long the partners had known each other before they started dating. They found that couples who paired up soon after meeting tended to be well matched in physical attractiveness, both rated similarly by outside observers. Couples who had known each other a long time first, or had been friends before dating, were far less matched on looks.

The interpretation, published in the journal Psychological Science, is that consensus about attractiveness is strong at first sight, when looks are almost all you have to go on, and weakens as people actually get to know each other. Given time, impressions become, in the researchers’ phrase, more unique and less consensual. Other qualities start to reshape who looks appealing to whom.

Put simply, when everyone is a stranger, we mostly agree on who is attractive. Once people know each other, that agreement quietly falls apart.

Why knowing someone rewires it

Two things seem to be happening as acquaintance grows.

The first is that familiarity keeps working on us. Seeing the same face repeatedly, in ordinary everyday contexts, tends to make it more likable, so proximity alone does some of the work that a striking first impression cannot.

The second is that character becomes visible, and it bleeds into how a face is actually seen. In studies where people are given information about someone’s personality, learning that a person is warm and likable raises how physically attractive they are then rated, while learning they are unpleasant lowers it. A 2004 study by Kevin Kniffin and David Sloan Wilson took this further, asking people to rate the looks of individuals they actually knew. How much someone liked and respected a person predicted how physically attractive they judged them to be, and there was strikingly little agreement between raters, because each was scoring a different history with that face.

This is not people being polite about it. The same face genuinely looks different depending on who you have learned is behind it. Attraction, in other words, is not read off a face once and filed away. It is continuously updated.

What this does and does not mean

None of this is a claim that looks do not matter. They clearly do, especially among strangers, on dating apps, and in the first few minutes of meeting, where there is little else to go on. The averageness and symmetry effects are real, and it would be dishonest to wave them away.

Nor is any of this advice. It is a description of how attraction behaves, not a method for becoming more attractive or choosing a partner, and I am wary of turning findings about groups into instructions for a life.

What the research does undercut is the premise hidden in the question. “What makes someone attractive” sounds like it should have a single answer located somewhere in a person’s face. For strangers, briefly, it almost does. For anyone you actually know, the answer moves. It becomes specific to you, shaped by familiarity and by everything you have learned about them, and it stops being a thing the rest of the world can agree on.

That is probably the more useful way to hold it. The people who end up mattering to us are rarely the ones a panel of strangers would have picked. They are the ones who became attractive to us in particular, which is a different thing entirely, and a far more forgiving one.