The Biochemistry of Affection: Love, Scientifically

Why do we do what we do when we get a case of the Lovesies…

Chemicals such as neurotransmitters, sex hormones, and neuropeptides are responsible for the behaviors humankind exhibits, as well as the moods they experience during attraction, dating, sex, and love. The effect of these chemicals is fairly intense, especially in comparison to the physiological effects of other moods. Time and evolution have conspired to create a scheduled release of various neurotransmitters, hormones, and other biochemicals over time to create a potent, and purposefully variable, set of emotions that gives humankind a drive that has the potential to be even stronger than the basic will to live. In each phase of the love process, different chemicals exhibit different physiological qualities at designated times.

1. The Honeymoon Phase: Lust

 The initial phase of love is driven by sex hormones, especially testosterone. Pheromones are also believed to play a part in physical attraction at this stage of love. Increased levels of norepinephrine and cortisol effect anxiety and accelerate the heart rate. Alternatively, the initial feelings of love can reduce the effects of stress and anxiety of everyday life by increased levels of dopamine. Dopamine is key to the perception of pleasure (and pain) throughout every phase of love. Jointly, all of these biochemicals “are secreted when we feel that initial attraction to someone, and function like an amphetamine, keeping our mood elevated, senses extra alert, and giving us the urge to bond and attach to others (Firestone, 1).”

2. The Love-High Phase: Attraction

The pictograms below illustrate how different moods affect the human body uniquely, with lighter areas of contrast denoting a more extreme physiological change as a result of positive or negative emotion.

These results are based on a private study of over 700 people from Northern Europe and China. Red and yellow areas show where on their bodies participants experienced an increase in sensation (warmth, tingling, tightness, etc.), and blue areas show where they experienced a decrease in sensitivity (i.e. coldness, numbness).Only happiness, pride and anger show similar results in increased intensity, while all other emotions have relatively mild sensation effects.
MRIs show that during the attraction phase, the pleasure center of the brain is active, resembling obsessive-compulsive brain activity caused by varying levels of serotonin and dopamine. Partners in this phase can become fixated and even co-dependent on one another for emotional and physical well-being. The secretion of dopamine while in the presence of the beloved cause a feeling of preference, elevating the person of interest to a special, aggrandized status. This also causes the lover to selectively place importance on those traits which are favorable, and easily overlook those which are not.
Dopamine, norepinephrine, and adrenaline are all at higher levels in the body during this phase, providing the euphoria, energy, agitation and preoccupation that are experienced during the early and mid-phases of the love experience.

3. The Long-Term Love Phase: Attachment

As a healthy relationship develops, a romantic couple eventually enters the attachment phase of love, in which a tolerance is developed to the highs and lows of the various hormones and pleasure stimulants of early romance. This usually occurs about 18 months to 2 years into the relationship, as the cycle of biochemical stimulation is ending. This plateau of emotion provides a more stable condition for the couple, and establishes “partner preference (Loyola, 2).” The urge to fixate and obsess on the partner lessens, and is replaced by a sense of security, calm, and well-being, and the lover’s mind begins to expand their idea of self to include their object of affection. This is due to a chemically timed increase of endorphins, vasopressin, oxytocin, and major histocompatibility complex.

4. Lovesickness and Limerence

 If an unhealthy (one-sided) attachment or relationship develops in place of mutual attachment, love-sickness occurs. Limerence, or love-sickness, is defined as an “involuntary cognitive and emotional state in which a person feels an intense romantic desire for another person (Lovelogica, 1).” Over time, it is typically harmless, but for certain personalities, can lead to serious physical and psychological problems. To the casual observer, the effects of love-sickness seem like infatuation and obsession. To a clinical eye, it resembles obsessive-compulsive disorder, bi-polar disorder, and psychosis. Limerence is a result of the decrease of the chemicals that caused the euphoric feeling of love. It has been compared to drug addiction and withdrawal, and results in physical pain, and abnormal – even extremely irrational – behavior. Limerence, like love, has the same first three stages of lust, attraction, and attachment, but, unlike a healthy, mutually loving relationship, is underlined by constant feelings of anxiety, loneliness and pain.       The implications of love-sickness to a person’s health is significant as well; those in “unsupportive and harmful relationships are at greater risk for developing heart problems, depression, and immune deficiency (Schwecherl, 1).” Love and limerence could be considered polar opposites, at their extremes, as best visualized by comparing the “love” and “depression” pictograms above.

The emotional high-producing chemicals of love and their effects are known to wane and disappear after six months to two years, like clockwork, after the man and woman in love have had sufficient time to mate and procreate. This would suggest that the euphoria experienced in love is mainly a function of biochemical evolution, encouraging procreation and therefore continuance of the species. Other theories suggest that long-term relationships are favored in terms of survival and health by reducing the incidence of STD infection between sexual partners. It has also been purported that stable, long-term relationships provide a consistently healthier environment in which to raise offspring. Even in the animal kingdom, fidelity has its advantages, giving young offspring a stronger, more secure, and therefore advantageous beginning in life as compared to young without the benefit of early parenting and protection.

Brain imaging studies have shown that at least 2 areas of the brain become more active when in love. The media insula and anterior cingulate cortex regulate instinct and euphoria, respectively. By this observation, it could be inferred that evolution has provided an instinctual need to be fulfilled by love, and has a built-in mechanism for reward by euphoria when achieved. By submitting to innate urges for sex, attachment and fidelity, the human being is rewarded with happiness, energy, overall physical and mental health, and healthier offspring.


Ackerman, Diane. “The Brain on Love.” The New York Times: Opinionator. The New York Times, Inc., 24 Mar. 2012. Web. 09 Nov. 2014.
Anthony, Sebastian. “Human Emotions, Mapped for the First Time.” Extreme Tech. Ziff Davis LLC, 31 Dec. 2013. Web. 08 Nov. 2014.
Deza, Danny. “How Love Changes Your Body Chemistry.” Health. Time Inc., n.d. Web. 09 Nov. 2014.,,20568672,00.html
Films for the Humanities and Sciences. The Science of Love. Films on Demand: Digital Educational Video. Films Media Group. 24 April. 2014. Web. 09 Nov. 2014.
Firestone, Allie. “The Physical Effects of Falling in Love.” Divine Caroline. Care2, 21 Feb. 2010. Web. 08 Nov. 2014.
Lovelogica Contributors. “Limerence and Unrequited Love: Are You Lovesick?” Lovelogica. N.p., n.d. Web. 09 Nov. 2014.
Loyola University Health System. “What falling in love does to your heart and brain.” ScienceDaily. ScienceDaily, 6 February 2014. Web. 08 Nov. 2014.
Martinez, Silvia. “The Chemistry of Love.” The Chemistry of Love. N.p., n.d. Web. 09 Nov. 2014.
Schwecherl, Laura. “The Surprising Health Effects of Love.” Greatist. Greatist, 14 Feb. 2012. Web. 08 Nov. 2014.
Tashman, Marty, Dr. “The Five Stages of Relationships.” Family Marriage Counseling. The Family & Marriage Counseling Directory, n.d. Web. 09 Nov. 2014.
Wikipedia Contributors. “Biological Basis of Love.” Wikipedia. Wikimedia Foundation, 11 June 2014. Web. 09 Nov. 2014.

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