Jealousy is a complex emotion that most people experience at some point in their lives. It can arise when there is a threat to a valued relationship, often from a rival. Jealousy can be triggered by a range of situations, from a partner showing interest in someone else to a friend spending time with other people. Even though it is a universal human experience, the inner workings of jealousy remain something of a mystery. In recent years, scientists have gained some insights into the biological basis of jealousy, including the key hormones involved.
The Role of Testosterone
One hormone that has been strongly implicated in jealousy is testosterone. Testosterone is considered the primary male sex hormone, although women also produce small amounts of it. In both men and women, testosterone levels have been shown to increase when they are exposed to jealous scenarios, such as images of their partner flirting with someone else.
In one study, scientists showed women either images of their romantic partner with another woman or neutral images with their partner alone. The images of their partner’s infidelity caused a spike in testosterone levels, while the neutral images did not. This indicates that testosterone may help drive jealous feelings and responses to perceived threats against a relationship.
Further evidence comes from studies on single men interacting with an attractive woman. When the woman seems romantically interested in another man present, the single men experience a surge in testosterone. This is likely an unconscious evolutionary response, as higher testosterone could potentially help men compete for mates and guard against reproductive threats.
In both men and women, higher baseline testosterone levels are associated with greater jealousy and mate guarding behavior in relationships. People with naturally higher testosterone also show stronger nervous system responses when exposed to signals of partner infidelity.
Testosterone is linked to dominant and aggressive behavior in both males and females. Therefore, researchers believe evolution has shaped human physiology to use testosterone increases to motivate jealous and protective responses. However, excessive jealousy and aggression obviously isn’t healthy and some people are more prone to extreme jealous reactions.
Estrogen’s Role
The role of testosterone in jealousy is quite well established, but more recent research has investigated the role of the female sex hormone estrogen. Some initial studies found that estrogen levels did not change much in response to jealousy-provoking scenarios.
However, further research has uncovered a more complex picture. It seems that estrogen may specifically influence how women cognitively process and respond to signals of partner infidelity. Unlike testosterone, estrogen levels do not necessarily increase but there are changes in how estrogen activity is regulated in the brain.
A study conducted at Georgetown University found evidence that estrogen modulates activity in brain regions involved in processing threats to social relationships. The study used functional MRI scans of women’s brains. When exposed to images depicting their partner’s infidelity, women showed increased activation of cortical regions involved in detection of threats and negative emotions. This response was stronger in phases of the menstrual cycle when estrogen levels were higher.
The researchers concluded that estrogen fluctuations may sensitize women to cues of social threats to relationships. However, they emphasized hormone responses are likely just one factor contributing to the complex neural basis of jealousy.
Oxytocin and Vasopressin
In addition to sex hormones, researchers have investigated how brain chemicals involved in social bonding may contribute to jealousy. Two key neuropeptides are oxytocin and vasopressin.
Oxytocin is released during social bonding and orgasm. It promotes affection, trust and communication between couples. In women, oxytocin levels spike after intimate physical contact with a partner. Oxytocin is thought to help suppress feelings of jealousy in healthy relationships.
Conversely, vasopressin activity increases when bonds are under threat. Vasopressin is linked to territorial behavior in animals and may play a similar role in humans. In men particularly, vasopressin may motivate protective responses when a partnership is jeopardized, although research is still exploring this hypothesis.
Dysregulation of oxytocin and vasopressin pathways in the brain may potentially contribute to excessive jealousy and associated behavior problems. However, more research is needed to confirm if they directly alter jealous responses.
Cortisol and Adrenaline
Two other important hormones released in response to stress are cortisol and adrenaline (epinephrine). Both are produced by the adrenal glands as part of the ‘fight-or-flight’ response triggered by threats.
Cortisol and adrenaline surge when someone faces a stressful or frightening situation to prepare them to respond. Research confirms both hormones increase when people imagine their partner being unfaithful.
In one study, male participants provided a saliva sample to measure cortisol and adrenaline levels. They were then asked to imagine their partner or spouse becoming attracted to another person. Following this jealous imagery, both hormones showed significant increases.
Cortisol and adrenaline help explain the emotional intensity and anxiety that often accompanies an acute jealousy response. Their release prepares someone physiologically to deal with threats to a valued relationship.
However, adverse effects can occur when cortisol and adrenaline spikes become chronic. Prolonged elevated levels have been linked to increased risk of mental health problems and health conditions.
Prolactin
Prolactin is a hormone that enables mammals to produce milk. However, it is secreted by both men and women and has wider effects. Research suggests prolactin may suppress sexual arousal and attraction when bonding in a relationship.
One study found prolactin levels increased in newly committed couples. The couples who showed greater prolactin rises also reported feeling less attraction to people other than their partner. Increased prolactin was also linked to reduced testosterone in men.
Through this mechanism, prolactin may help prevent jealousy by decreasing interest in alternative partners. Higher prolactin activity during bonding and childrearing may have evolved to strengthen family structures and paternal care.
However, the links between prolactin and jealousy still need more investigation. Some researchers propose that abnormally low prolactin reactivity could potentially indicate relationship problems or difficulty bonding.
Gender Similarities and Differences
While men and women both experience jealousy, researchers have explored whether biological responses differ between the sexes. Many studies have focused on how testosterone versus estrogen influences jealous reactions.
Findings overall show more similarities than differences. Both men and women show testosterone increases, and estrogen changes, in response to partner infidelity threats. However, some research indicates men may show greater surges in testosterone, while women show more complex estrogen effects.
Brain scanning studies have identified a broadly similar neural circuitry underlying jealousy in both sexes. However, men appear to activate more vasopressin-related brain regions when exposed to relationship threats.
In terms of behavior, both men and women report becoming more vigilant and protective. However, men are more likely to display overt possessive actions, while women tend to conceal their jealousy more.
Culture and social expectations also influence how jealousy is expressed between genders. But fundamentally, men and women share the same core goal of preventing harm to valued relationships and offspring.
Individual Differences
While key hormones underlie jealousy in all people, there are substantial individual differences in responses. Some people experience much more intense or irrational jealousy than others, even given similar situations.
These individual variations are shaped by the interaction of biological factors, personal history, and social influences. People with certain personality traits, attachment styles, and tendencies toward obsession or anxiety report greater jealousy.
Upbringing also plays an important role. People who witnessed infidelity or abandonment as children, or were raised to expect it, often feel higher jealousy. Abuse and trauma can likewise amplify tendencies toward pathological jealousy.
Irrational or excessive jealousy negatively impacts relationships when it becomes controlling behavior. In some cases, counseling or psychotherapy may be helpful to overcome past trauma or anxieties fuelling jealousy.
Conclusion
Jealousy emerges from an intricate interplay of hormones, brain pathways, psychology and experiences. Key hormones like testosterone, estrogen, cortisol and prolactin shape biological responses to relationship threats. But individual differences and social factors modify the behaviors jealousy ultimately produces.
While jealousy itself is neither good nor bad, excessive or irrational expressions of it can harm relationships. Learning to communicate openly and honestly with partners is important for keeping jealousy at bay. With self-awareness and empathy, people can experience jealousy as an occasional natural emotion rather than a destructive force.
