A lot of initial attraction is based on visual cues, but just ask anyone who's ever used Tinder and they'll tell you: looks ain't everything. So forget love at first sight; let's talk about love at first prolonged, close-up armpit sniff. Because while you might think you want all kinds of qualities in a mate—floppy hair! trivia skills! a vast collection of striped button down shirts!—smell can actually be one of the simplest predictors of attraction*.
All of us, without knowing it, are capable of literally snorting our ways to a good mate. This is because we unconsciously "smell" chemical signals in our environment, including the components of other peoples' body scents. In fact, we have individual odors the same way we have unique fingerprints. Like stinky lil chemical snowflakes.
Smelling someone's B.O. gives us info about their personal major histocompatibility complex (or MHC), and kids whose parents have somewhat dissimilar MHCs are immunologically healthier. So when someone smells all sexytimes good to you, it might actually be your olfactory bulb screaming "YOU GUYS SHOULD TOTALLY HAVE BAYBEEEEEES." Which...inappropriate, olfactory bulb. Maybe I'm not ready to be a mom; did you think about that before sending a bunch of chemical signals to my brain indicating I should make out with this guy? No, no you did not. It's the same regardless of orientation or gender—a dissimilar (but not too dissimilar) MHC is associated with smelling more pleasant and attractive.
The only people for whom this isn't true, actually, are women on The Pill. Birth control actually changes who you're attracted to, with women preferring people whose MHCs are more similar to their own. So someone you thought was cute when you were taking Yaz may be significantly less charming when you go off it.
Which brings us to perhaps the most fascinating part of this whole thing for beauty fans: the genetic basis for having a signature scent. Turns out we probably love fragrance so much because we're actually using it as an MHC amplifier to help mates find us. Wearing that Byredo is like holding up a megaphone to your genes and hoping someone who really, really likes them will follow the scent trail straight to you. If there was ever an argument for buying the scents you like instead of just whatever's popular...well, this one's pretty definitive.
*The science of scent is fascinating, but before we go any further I should say that I'm covering this in a very, very cursory way. There's plenty of disagreement in the biological community about how much humans use olfactory data, so I've tried to take information from recent, reputable studies, with some additional theories offered because they're interesting and fun to consider!