How to tell you're in love with someone, according to science

Is there a special someone you just can't get out of your head? Do you find yourself daydreaming about them when you should be working or studying? Does it feel different this time?

Well, you might be in love — but how can you be sure? Interestingly, scientists have made a lot of progress in understanding what love is and have started to pin down what it means to "fall in love." The brain of a person in love looks very different from one experiencing a platonic relationship or simply lust, and studies led by Helen Fisher, a senior research fellow at the Kinsey Institute at Indiana University, and other researchers have identified psychophysiological characteristics often associated with the phenomenon.

Keep in mind that scientific studies have historically focused on monogamous, heterosexual relationships, so they're not necessarily relevant for everyone. A small 2010 study published in the journal PLOS One, however, found that the brains of heterosexual people and homosexual people responded the same way to seeing their beloved partners, and it found no difference between men and women included in the research.

With that said, here are 14 telltale signs you're in love, according to science.

Related: Why does heartbreak hurt so much? Science has the answer

Special meaning

When you're in love, you begin to think your beloved is special and can become a bit obsessed with them. Fisher told Wired in 2022 that the first thing to happen when you fall in love is that the person takes on special meaning, contrary to a platonic — meaning nonromantic — relationship. Everything about the person you're in love with becomes special, such as their car, house or taste in music.

"When you're madly in love with somebody in a romantic attraction, you are obsessed, and in a platonic attraction, you don't think about them night and day," Fisher said.

Focus on the positive

People who are in love tend to begin to idealize their partners, focusing on the positive qualities of their beloved while overlooking their partner's negative traits. It's not clear whether this is necessarily a good thing in long-term partnerships. A 2011 study published in the Journal of Family Theory & Review looked at studies about idealization in relationships and couldn't determine whether it was a good predictor of marital satisfaction.

Fisher's research has suggested that those who are in love also focus on trivial events and objects that remind them of their loved one. She found that most men and women reported recalling trivial things that their partners said and did, and they would also replay these moments in their heads.

This focused attention is also thought to result from elevated levels of the chemical messenger dopamine in the brain and spinal cord, as well as a spike in norepinephrine, a chemical associated with increased memory in the presence of new stimuli, particularly emotionally arousing stimuli.

Emotional instability

As is well known, falling in love often leads to emotional and physiological instability. When extreme, these mood swings can somewhat parallel the behavior of people with substance use disorders, in that the need to seek out and be with the person can prompt harmful behaviors, according to a 2017 article in the journal Philosophy, Psychiatry, & Psychology.

Fisher has argued that romantic love should be considered akin to an addiction — but that "love addiction" is positive when the love is reciprocated, nontoxic and appropriate, and negative when the opposite is true. "Symptoms" of love addiction include cravings, withdrawals and relapses, similar to drug dependence, she argues.

Intensifying attraction

Going through adversity in a relationship can intensify romantic attraction, according to Fisher's research. For example, separated lovers may experience anxiety if they aren't able to see each other, and they show elevated dopamine levels when reunited. That's because when a reward of dopamine in the brain is delayed — in this case, through separation — the dopamine-producing neurons in the so-called midbrain become more productive. In other words, absence really can make the heart grow fonder.

It's worth noting that people also put more time into their platonic relationships when separated. A 2017 study published in the journal EPJ Data Science found that people spend longer on the phone with someone when the time between their calls is increased, so it's not just lovers who are affected by separation.

Related: Brain signature of desire uncovered in lovesick rodents, and it may be in people, too

Intrusive thinking

People who are in love can spend a lot of time thinking about their partners. One small study of 10 women and 7 men who reported having recently fallen madly in love reported spending more than 85% of their waking hours musing over their beloved, according to a 2016 study published in the journal Frontiers in Psychology.

Being in love also prevents people from focusing on other information, according to a study published in 2013 in the journal Motivation and Emotion. The researchers found that passionate love among students correlated with decreased efficiency and worse performance on tasks provided by the researchers.

Emotional dependency

People in love regularly exhibit signs of emotional dependency in their relationships, including possessiveness, jealousy and fear of rejection. For instance, Fisher and her colleagues looked at the brains of individuals viewing photos of someone they were still in love with despite being rejected by that person.

The study involved only a small sample of rejectees, but brain scans taken using functional magnetic resonance imaging (fMRI) showed activation in several brain areas, including forebrain areas such as the cingulate gyrus, that have been shown to play a role in cravings in people addicted to cocaine. Broadly speaking, the brain's reward system lights up in anticipation of a variety of rewarding stimuli — from food to social interactions to sex — so this overlap isn't necessarily surprising.

"Activation of areas involved in cocaine addiction may help explain the obsessive behaviors associated with rejection in love," the researchers wrote in 2010 in the Journal of Neurophysiology.

Planning a future

Longing for an emotional union with a beloved, seeking out ways to get closer, and daydreaming about a future together are also signs of love. According to an article in The Harvard Gazette, when the brain's serotonin levels begin to return to normal levels after spiking at the start of a relationship, the hormone and neurotransmitter oxytocin increases in the body. This chemical messenger is associated with more mature relationships and helps cement pairings, research suggests.

Lucy Brown, a neuroscientist at the Albert Einstein College of Medicine in New York, told Live Science in 2011 that the drive to be with another person is sort of like our drive toward water and other things we need to survive.

"Functional MRI studies show that primitive neural systems underlying drive, reward recognition and euphoria are active in almost everyone when they look at the face of their beloved and think loving thoughts," Brown said. "This puts romantic love in the company of survival systems, like those that make us hungry or thirsty.

"I think of romantic love as part of the human reproductive strategy," she added. "It helps us form pair-bonds, which help us survive. We were built to experience the magic of love and to be driven toward another."

Feelings of empathy

People who are in love have a great deal of empathy for their partner, feeling the other person's pain as their own and being prepared to sacrifice anything for the other person, according to Fisher's research.

That empathy is a good thing, too, because showing your partner that you care about them can benefit the relationship. For example, empathy can motivate supportive behaviors that help alleviate a partner's suffering during difficult times, as well as help a partner celebrate their successes, according to a 2017 study published in the Journal of Social and Personal Relationships.

Related: Humans can 'smell' each other's emotions — but we don't know how

Aligning interests

Falling in love can result in someone reordering their daily priorities to align with those of their partner. While some people may attempt to be more like a loved one, another of Fisher's studies, presented in 2013 at the "Being Human" conference, found that people can be attracted to their opposites, personality-wise.

For instance, her research found that people who were highly analytical, competitive and emotionally contained were often drawn to mates with personalities who tended to be "empathetic, nurturing, trusting and prosocial, and introspective, seeking meaning and identity," Fisher said in 2013.

(Using past research, Fisher theorized that these personality types are tied to specific hormones in the body, such as testosterone or estrogen, but she didn't directly assess the levels of these hormones in people surveyed for the paper.)

Possessive feelings

Those who are deep in romantic love often experience sexual desire for their beloved, but there are strong emotional strings attached: The longing for sex in many lovers can be coupled with a desire for sexual exclusivity and jealousy at the prospect of infidelity.

According to a 2011 study in the Indian Journal of Endocrinology and Metabolism, oxytocin is released during sexual activity. This hormone creates social bonds and develops trust. Oxytocin is also sometimes called the "cuddle hormone" or "love hormone" because it's released when people snuggle, but this is a little misleading because it's released in a variety of other scenarios, too, including when people play with their pets.

Craving an emotional union

While research suggests that the desire for sexual union is important to many people in love, it's not the be-all and end-all. In fact, Fisher's 2002 study published in the journal Archives of Sexual Behavior found that 64% of people in love — the same percentage for men and women — disagreed with the statement "Sex is the most important part of my relationship with [my partner]."

The longing for an emotional union is often reported as the most important factor in relationships and appears to supersede sex. Furthermore, while rejection in love can trigger protest and rage, these behaviors can then move into resignation and despair, according to a 2016 study published in the Indian Journal of Endocrinology and Metabolism.

Out-of-control feelings

Fisher and her colleagues found that individuals who report being in love commonly say their passion is involuntary and uncontrollable. For her book "Love and Limerence: The Experience of Being in Love" (Scarborough House, 1998), psychologist Dorothy Tennov asked 400 men and women in Connecticut to respond to 200 statements on romantic love. Many participants expressed feelings of helplessness, saying their obsession was irrational and involuntary.

Loss of the spark

The initial state of being in love doesn't always last forever. It's often an impermanent state that either withers and dies or evolves into a long-term relationship that psychologists call "attachment." When this happens, your cortisol and serotonin levels return to normal, and the negative, stressful aspects of love, such as anxiety, tend to go away, according to Harvard Medical School.

If there are physical or social barriers inhibiting partners from seeing one another regularly — for example, if the relationship is long-distance — then the intense romantic love phase generally lasts longer than it would otherwise.

Fisher and colleagues published a 2012 study in the journal Social Cognitive and Affective Neuroscience that found that, for some individuals, the activation in reward pathways in the brain seen in new love may even be sustained in long-term relationships coupled with attachment. In other words, you can be madly in love with someone for decades, if you're lucky.

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Hypomania

Several studies have found that the early stages of intense romantic love are associated with hypomania, a period of elevated mood levels where people can also experience things like increased energy and confidence, as well as increased irritability and disinhibition, all while sleeping less. (This is not to be confused with hypermania, which ramps this up to a higher intensity and has additional effects.)

A 2007 study published in the Journal of Adolescent Health found that young lovers around 18 years old scored higher on a scale of hypomania, with increased positive-mood states in the mornings and evenings, compared with those who were uncoupled. A 2015 study in the International Journal of Psychiatry in Clinical Practice suggested romantic love was not entirely joyful, though, and also came with the darker sides of hypomania, including poor sleep quality.

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