At this point in our lives, we're all pretty familiar with the kinds of people to whom we're attracted.
We have a preferred hair color, a preferred personality type, and a set of deal-makers ("You hate Pitbull, too?!") and deal-breakers ("His breath smells like someone crawled into his mouth and died. I can't.").
Or, maybe we don't have any of those things. Hell, maybe we know what we don't like -- but that's also kind of like knowing what we do like, right?
Anyway, all of these basic determinants of attractiveness -- smelling good, looking good and having an awesome personality, for example -- are effective in helping us figure out who we want to date.
However, there are other strange rules of attraction that operate on a deeper, more unconscious level that help us out, too.
So, if you aren't sure what you like, you may be relying on one of these ten things without even knowing it.
1. What you eat
AYI analyzed the activity of its 180,000 app users (totaling 2.4 million interactions overall) and found that diet played a role in whether or not a user would reach out to contact someone.
Women were 13 percent more likely to contact meat-eaters than vegetarians; on the contrary, men were 11 percent more likely to contact vegetarians than meat-eaters.
Looks like the hamburger-eating-"Cool Girl" trope fails here -- men want women to eat salads!
I'm joking. But seriously.
2. Mouth germs
There are billions upon billions of bacteria in our bodies. In fact, the ratio of bacteria cells to human cells is a whopping 10 to 1, so it makes sense that germs have something to do with an important bodily function, like attraction.
In a November 2014 study, Dutch researchers found that couples had similar mouth germs, or "microbial communities," on their tongues.
They surveyed 21 couples about how frequently they kissed and when their last kiss was. After, they swabbed their mouths and discovered the similarities.
Then, they asked couples to engage in a 10-second kiss, and then swabbed their mouths once again to determine microbial community makeup.
The kiss did not lead to a significant additional increase in microbial community similarity, indicating that the microbial community makeups were similar, even without an immediate swapping of bacteria.
In addition, in regards to the survey, tongue-germ similarity did not clearly correlate with kissing behaviors, which suggests a variety of other reasons for similar bacteria on the tongue. Perhaps, the reason is love, huh?
3. The presence of tears
In a 2011 study, researchers found that tears made men less sexually attracted to women.
They had a group of men sniff "negative-emotion-related odorless tears" and then look at a variety of photos of women's faces.
Upon looking at the photos, the men experienced reduced levels of testosterone, reduced levels of both physiological measures of arousal and of self-reported arousal -- all from the presence of these tears.
No word on whether or not women's libidos were affected by male tears. I'd like to assume the modern woman enjoys a sensitive man, so tears would turn her on. But, who knows? I'm not Science.
4. Body odor
B.O. plays a significant role in levels of attraction. Normally, women prefer the body odors of men whose major histocompatibility complex (MHC) genes differ from their own, and one of the ways you can detect MHC is through body odor.
This evolutionary rule of attraction benefits men, as well: The more similar MHC genotype between couples, the lower their sexual attraction towards each other.
So, when your girlfriend nuzzles up against you after you just came home from the gym, be grateful. It means your sex life is awesome.
5. Birth control
Research has suggested that women who take the pill prefer men with less masculine faces, like rounded faces and narrower jawbones.
Additionally, as we know, women normally prefer men whose MHC genes differ from theirs, but birth control switches women's preferences to men who have similar MHC composition.
Therefore, if you start taking the pill mid-relationship, beware of that switch in scent preference; it could affect how attracted you are to your partner. (Though, if it makes you feel any better, my ex-boyfriend was afraid this would happen to us when I started the pill while we were dating, and it didn't at all.)
Birth control also affects how a woman views her man as a sexual partner and as a father.
If a woman was on birth control when she chose her partner, she reported having less attraction as more likely to initiate a breakup (if it were to occur), and as having experienced decreasing sexual satisfaction.
These same women, however, felt more satisfied with their partners' potential as a father, meaning, despite the decline in sexual attraction, their relationships were longer and the women had no intention of splitting up.
All of this indicates that use of birth control could influence family relationships, reproductive behavior, and overall quality of romantic and sexual life.
6. His/her name
At the Edinburgh International Science Festival in 2008, psychologist Richard Wiseman conducted what he called "The Name Experiment": He surveyed 6,000 people to determine what names they found most attractive.
Women had stronger opinions than men about what names they found attractive. Women thought Ryan, James and Jack were the top three hottest names, and the ugliest were Peter, Thomas and George.
For men, Sophie, Rachel and Olivia topped the list as the three most attractive, and Helen, Jane and Ann were the least attractive.
Sorry, Romeo, but that which we call a rose by any other name doesn't actually smell as sweet.
7. What your parents look like
A study from the University of St. Andrews found we are more inclined to date people who have the same eye color and hair color as our opposite sex parent.
Researchers speculated a variety of reasons why. It could be because human beings are naturally drawn to what's more familiar, and eye and hair color we've seen before indicates familiarity.
It could also just be a consequence of how we learned to visually recognize our parents.
Don't worry, though. This doesn't mean you're attracted to your dad.
Everyone looks better in sunglasses.
Vanessa Brown, a senior lecturer of art and design at Nottingham Trent University, told New York Magazine sunglasses conceal any kind of asymmetrical imperfections on our faces, and studies have shown human beings are attracted to faces with more symmetry. Adding sunglasses instantly makes a face more symmetrical.
Additionally, sunglasses add an element of mystery to our faces. We tend to make judgments with our eyes, so if your eyes are covered, nobody can tell exactly how you're feeling, which makes you a more intriguing person.
And, an air of mystery has been shown to increase sexual desire, too.
As if you needed any more of a reason to splurge on those new Ray Bans.
9. If you're wearing red
The color red operates at a uniquely subconscious level. A 2008 study suggests men find women who wear red more sexually desirable and attractive.
Red didn't, however, indicate how men perceive women's intelligence, kindness or likability.
Until 2010, it had been previously assumed only men were seduced by the red effect, but it appears as though red affects women, as well.
A 2010 study showed women preferred men who were wearing red or who were framed in red.
I guess Christian Grey was onto something when he named his BDSM dungeon, "The Red Room."
10. How adrenaline-inducing the activity you're doing together is
Research has suggested that when a couple engages in an adrenaline-inducing activity, they are more likely to be attracted to each other.
The relationship was very positively correlated: As levels of adrenaline during an activity increased, feelings of attraction increased, as well.
This is probably how "The Bachelor" successfully manipulates people into falling in love. A recipe for love includes two strangers and a helicopter ride over the Grand Canyon, apparently.