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Science of Love: Oxytocin and Other Love Chemicals

Crystal Risko
Product Developer

For centuries, scientists and philosophers have been trying to understand the phenomenon of falling in love. What is it about that special someone that makes them so attractive? What keeps people together long after the sparks start flying?

Although many questions remain unanswered, much has been discovered about the chemicals behind falling in love. Biological anthropologist Dr. Helen Fisher, a member of Rutgers University’s Center for Human Evolutionary Studies, describes love as having three stages—lust, attraction, and attachment. Specific chemicals characterize each of the stages.

Stage 1: Lust

We typically associate males and females with their own distinct hormones: testosterone for males, and estrogen for females. However, both genders have both hormones. Studies have shown that when men fall in love, their testosterone levels decrease, whereas when women fall in love, their testosterone levels increase. These changes seem to disappear later in the relationship. Some scientists have suggested that changes in hormone levels exist to make the individuals more similar. Men with lower testosterone levels also tend to be more involved in childcare. Both estrogen and testosterone levels play a role in attractiveness and sexual interest.

Stage 2: Attraction

Serotonin is a neurotransmitter thought to be involved in feelings of wellbeing and happiness. This explains why many antidepressants reduce the reabsorption of serotonin, increasing its levels in the blood. In those first falling in love, the levels of serotonin decrease, falling to levels similar to those seen in individuals with obsessive compulsive disorder. This may explain the anxious feeling and obsessive thinking often characterized in this stage of relationships. However, according to studies, later stages show higher levels of serotonin, which are associated with happiness and calm.

Dopamine is a neurotransmitter, a chemical that transmits signals from one neuron to another. Its presence in the mesolimbic pathway (also known as the reward pathway) makes it a key player in the biochemistry of addiction. In couples newly in love, studies have shown high levels of dopamine. A surge in dopamine may be responsible for some of the symptoms of new love, such as decreased appetite and intense interest in the small details of a relationship.

Epinephrine (Adrenaline) and cortisol are hormones that are released in response to stress. Falling in love tends to cause the body to exhibit a stress response. This produces the common side effects associated with love: excessive perspiration, racing heart, and dry mouth. 

Stage 3: Attachment

Oxytocin is a hormone produced by the hypothalamus and secreted by the pituitary gland. Often referred to as the love hormone, it is involved in maternal care, social bonding, happiness, and trust. Oxytocin may be partially responsible for monogamous relationships.

Prairie voles (Microtus ochrogaster), a model organism for monogamous relationships, have more receptors from oxytocin than do their closely related, more promiscuous counterparts the montane voles (Microtus montanus). Some studies have shown that when montane voles are given oxytocin and vasopressin, they become monogamous like prairie voles.

Vasopressin is a hormone responsible for regulating the body’s retention of water, allowing the body to maintain appropriate concentrations of dissolved solids in extracellular fluid. T

A study showed that when prairie voles were given an antagonist that blocked their vasopressin receptors they stopped their monogamous behavior. Further studies have shown that a related specied of vole, meadow voles (Microtus pennsylvonicus), have fewer vasopressin receptors than the prairie voles. When the number of vasopressin receptors in the brains of meadow voles were increased, they become monogamous.

Scientists believe this monogamy stems from the activation of a reward pathway during mating. The resulting release of vasopressin causes the meadow voles to feel happy about the mating partner they’ve chosen and encourages them to stick with that mate.

Although we still have much to discover about the phenomenon of falling in love, this much is clear: science plays a significant role. Those feelings of attraction are called chemistry for a reason.