Romantic love is the most extraordinary human feeling and is associated with health and happiness in adults. Romantic relationships thus have an important contribution to adult life. Well-functioning ones are associated with physical and psychological health. Unreciprocated love, on the other hand, may cause a variety of negative emotions. Also relationships themselves may be accompanied by stress, negative emotions and tension.

Romantic love only recently became a topic of experimental science. Until 20 years ago, it was thought that investigating feelings in general was not connected to science; rather research should investigate ‘real’ disorders. Moreover, would the magic of love not be taken away when you make it a topic of research?

It is now known that romantic love is associated with many hormonal changes. Several neurological hormones, including oxytocin, cortisol, and testosterone, are involved in both the initial period of love as well as in long-term relationships. The aim of this article is therefore to present an overview of the hormonal changes in heterosexual couples: new lovers vs. long-term partners.

The initial period of love

Falling in love is a complex process established by dynamic biological processes. It is characterized by various endocrine functions, which will be discussed in the following sections.

Predictor of relationships

Oxytocin, also known as the ‘cuddle hormone’, increases during the initial stage of romantic love. Remarkably, couples that stay together after this first period show even higher levels of oxytocin. The high level of oxytocin during the initial period of a romantic relationship thus has a positive effect on the process of partner attachment. This suggests that oxytocin may give an indication of the relationship’s duration.

Stressful condition

When we take cortisol, the ‘stress hormone’, into account, the process of falling in love is actually best described as a stressful condition. Research demonstrated that cortisol levels of both men and women who had recently fallen in love were significantly higher compared to those of men and women in established relationships.¹ Moreover, during the early stage of romantic love, women showed increased levels of cortisol compared to men. As entering a new relationship often brings many changes, it could also be that these increased levels are simply associated with fear of news things.

Libido and more

The last hormone to have a closer look at is testosterone. Testosterone is known as the male sex hormone. However, it is also made in small amounts in the woman’s body. A recent research measured the levels of testosterone in both men and women who had recently fallen in love in the previous six months, and compared these to subjects who were either single or in a long-term relationship.¹ It was found that testosterone levels are lower in men who had recently fallen in love compared to the other men. And interestingly enough, women who had just fallen in love have increased testosterone levels. It is therefore suggested that the stage of falling in love is associated with converging hormone levels. This could be a mechanism of temporally eliminating some differences between the sexes. The softening of male characteristics, like sex drive and aggression, due to testosterone, and the strengthening of the same characteristics in women may contribute to pair bonding in romantic relationships. An increase in testosterone results in an increase in sexual behaviour in women, which is typical for the first period of love.

The long-term relationship

Hormonal changes are not only important in the first stage of love. This relative short phase of “being in love” usually lasts only around several weeks to some years and evolves into a longer phase of “passionate love”, in which commitment and intimacy become important factors. There are, however, couples known who can hold the first period of love for a much longer time. In all monogamous long-term relationships, changes in hormone levels are still occurring.

Cuddles have long-term effects

As shown before, oxytocin plays an important role during the initial period of romantic love. However, oxytocin also contributes to pair bonding during long-term relationships. When men were treated with oxytocin, they described their female partner’s face as more attractive compared to unfamiliar women.² Increased levels of oxytocin thus lead to a desire for the partner. As oxytocin makes partners more attractive and improves the interaction between couples, this hormone is beneficial to couples in long-term relationships. Moreover, it may be possible to introduce oxytocin treatments for couples with relationship issues.

Temporary separation

The role of cortisol in long-term relationships is mainly associated with separation of romantic partners. In romantic partners who were in a long-term relationship, high levels of anxiety were linked to high levels of cortisol when the partners were separated.³ Regular contact with partners is important for day-to-day effect regulation of romantic love. Some researchers have even suggested that regular contact is intended to regulate partners’ physical and psychological state. A study investigating the changes in cortisol as result of temporary physical separations, such as those caused by work-related travel, exemplifies this idea. The researchers found significant changes in levels of cortisol from pre-separation to separation and from separation to reunion.³ Separation is thus a stressful business.

The less the better

Interestingly, the relationship status of men influences their testosterone status. Studies suggest that long-term relationships are associated with reduced testosterone levels.⁴ Men in more established relationships, for example, have lower testosterone levels compared to men in new relationships. Low testosterone levels of both men and women in long-term relationships will lead to commitment and relationship satisfaction. High testosterone levels, on the other hand, are often associated with attracting sexual partners. This is in general considered as being beneficial for sexual relationships, but not for long-term relationships. For people in a relationship lower levels of testosterone are beneficial.

Conclusion

Taken together, the findings in this paper about romantic love indicate that falling in love is a process accompanied by many hormonal changes. The establishment of romantic pair bonding, in the form of a long-term relationship, is also associated with changes in several hormone levels. Thus, both new lovers and long-term partners have to deal with flying hormones during different stages of their relationships.

Understanding the biological roots of romantic love will never take away the wonderful feeling that fulfils us when we love and are being loved. Instead, it will increase the potential to support our romantic relationships and provides us with more information about the biological mechanisms underlying such a special process.