Extradyadic Sex

Robin R Milhausen & Kristen P Mark. Encyclopedia of Human Relationships. Editor: Harry T Reis & Susan Sprecher. 2009. Sage Publication.

Extradyadic refers to a wide range of behaviors occurring outside of a committed relationship. Most research focuses on vaginal sex occurring outside of a marital relationship. However, behaviors can range from intense emotional relationships or close friendships, to kissing, oral sex, or other sexual behaviors, and the primary dyad need not be married. Extradyadic behavior that takes place on the Internet is a burgeoning area of research, focusing on individuals who engage in secretive, often sexually charged interactions with others online. Extradyadic relationships are often characterized as emotional or sexual in nature. Emotional relationships involve an intense friendship or romantic bond, but lack a physical or sexual component. Sexual relationships are considered to be purely physical, without emotional connection or commitment. Some researchers have suggested that infidelity more often exists on a continuum of sexual and emotional involvement.

A distinguishing feature of infidelity is that it occurs without the awareness or sanction of one’s partner. If both partners are aware of and consent to extradyadic activities, such an arrangement would be considered an open marriage or relationship; these types of relationships are more common among gay men but do also occur among heterosexual couples and lesbians. Unless otherwise stated, extradyadic sexual intercourse among heterosexual and same-sex couples, not condoned by both members of the primary dyad, is the focus of the current entry. Infidelity, extramarital sex, extrarelational sex, affairs, cheating, and adultery are other terms used to describe this type of extraextra-dyadic sex. In this entry, the prevalence of and attitudes toward infidelity will be described as will decisions about ending affairs, followed by correlates of infidelity and emotional and relationship outcomes. Finally, therapeutic implications and methodological issues are discussed.


Studies of infidelity among heterosexuals conducted during the past several decades suggest that between 20 and 40 percent of men and between 20 and 25 percent of women have ever engaged in extramarital affairs. In one study, 45.2 percent of gay men who indicated that they were in committed, monogamous relationships reported that they or their partner had sex with a third party since the beginning of their relationship. Data from national, representative samples, however, such as the 1994 General Social Survey and the National Health and Social Life Survey, suggest lower rates of infidelity. Specifically, data from national surveys indicate 23 to 25 percent of men and 12 to 15 percent of women have ever engaged in extramarital sex, with between 1 and 4 percent doing so in the past year.

Attitudes toward Infidelity

Results suggest that attitudes toward infidelity are most often negative, although men report more favorable attitudes than do women. Men and women typically evaluate infidelity in committed dating relationships less negatively than infidelity occurring among married couples. Some research suggests that women are more accepting of sexual infidelity than of emotional infidelity, and men are more accepting of emotional infidelity than of sexual infidelity. In general, however, emotional infidelity is more accepted than sexual infidelity is.

Correlates of Infidelity

Much of the infidelity research has focused on correlates of transgressing behaviors. The most widely cited predictors and correlates of infidelity can be broken down into three subcategories: demographic factors, interpersonal factors, and individual factors. However, study results vary widely; as a result, clear predictors of infidelity are difficult to determine.

Demographic Factors

Gender is the most commonly studied demographic factor. Gender is so critical in infidelity research that most researchers separate men and women in their analyses. Findings generally suggest that gay and heterosexual men are more likely to engage in infidelity and have more extradyadic partners than are women. However, when extra-dyadic behaviors other than sexual intercourse are considered (e.g., maintaining an intimate emotional relationship or engaging in other extrady-adic sexual behaviors), women report engaging in as many or more acts of infidelity than do men. Generally, men who engage in infidelity are motivated by sexual factors and women are more emotionally motivated.

Research on marital status suggests that married individuals are less likely to be unfaithful than are those who are cohabiting or dating. Perhaps level of commitment in a marriage relationship confers some protective benefit. Individuals who have had a divorce are more likely to have engaged in infidelity.

Race is also commonly included in correlational studies of infidelity, although the relationship between race and infidelity is not consistent. Infidelity appears to be more common among African-American persons, and particularly African-American men, than among other ethnic groups.

Religiosity is another demographic variable that is widely cited as a predictor or correlate of infidelity. Virtually all religious groups condemn extradyadic relationships and hold fidelity as a strong core belief. Infidelity is reported more often by individuals who endorse no religious affiliation than by those who endorse a religious affiliation. The interconnected nature of religious communities may decrease opportunities for infidelity and suggest to individuals that they are likely to be caught—two factors that may lessen motivation to be unfaithful.

Higher levels of completed education are often concomitant with more accepting attitudes about infidelity, but the relationship between education and extradyadic sexual behaviors is less consistent. Several studies have found that well-educated persons are more likely to engage in infidelity than are individuals with lower education levels. However, other studies have found the reverse, or no relationship at all. It is likely that the relationship between education and infidelity is a complex one, influenced by other factors.

Several demographic factors, such as employment, income, and rural versus urban residence, are thought to increase infidelity by providing individuals with greater opportunity to meet potential partners. Studies of couples or individuals in therapy suggest that 46 percent to 62 percent of persons who had engaged in extrarelational sex reported meeting their extradyadic partner through their workplace. Also, higher income levels can defray costs associated with infidelity and provide more opportunities to engage in extradyadic relations. Nonetheless, a number of empirical studies have not found a relationship between employment, income, and infidelity, and some find a relationship for men but not women. Results indicate that individuals who live in urban settings are more likely to engage in extradyadic relations than are those who live in rural areas. This could be attributed to a greater number of available partners in urban settings, as well as to a potentially lowered risk of discovery.

Interpersonal Factors

A variety of interpersonal factors increase the probability of being unfaithful. The strong expectation of fidelity in monogamous relationships levies high costs for being caught engaging in extradyadic relations. However, if the quality of the relationship is low, there is less to be lost as a result of infidelity. The interpersonal factor that best predicts infidelity in monogamous relationships is a lack of satisfaction in the primary relationship. In one study of gay men, participants in committed, monogamous relationships who reported that they, or their partner, had engaged in sex with someone else since the beginning of their relationship scored lower on measures of relationship quality and satisfaction than do men who maintained faithful monogamous relationships and men who had agreements with their partner to be sexually nonexclusive. Additionally, men and women who are sexually dissatisfied in their primary relationship are more likely to be unfaithful than are those who report sexual satisfaction, although sexual dissatisfaction plays a larger role for men than for women.

A number of other relationship factors have been found to put couples at risk for infidelity. For example, boredom, low levels of commitment, and higher levels of conflict in the primary relationship are associated with infidelity in both men and women. Perceived inequity also affects the likelihood of engaging in extradyadic sex, particularly among women.

Personal peer groups may also play a role in infidelity, especially for men. Individuals involved with a peer group where the prevalence and acceptance of infidelity is high are more likely to engage in infidelity themselves. Conversely, if there is a greater chance that members of a shared peer group will find out about extradyadic relations, men and women are less likely to engage in such behaviors.

Individual Factors

Personality attributes such as extraversion, low agreeableness, high neuroticism, low conscientiousness, and high psychoticism all contribute to a greater likelihood of engaging in extradyadic relations. Likewise, individuals who emphasize independence from their primary partner, those who feel a need for variety in their relationship, and those who feel insecure in their primary relationship all show higher incidences of engaging in infidelity. Men who feel a sense of powerlessness, meaninglessness, or social isolation tend to engage in more infidelity.

Psychological problems may also play a role in engaging in infidelity. In particular, individuals with low self-esteem or depression may be more likely to have extradyadic sex. However, one non-clinical study found that men who engaged in infidelity actually had higher self-esteem than did those who did not, and men and women who engaged in infidelity self-rated their attractiveness higher than did those who did not engage in infidelity. Additionally, those with substance abuse problems are more likely to engage in extradyadic relations. Notably, many results in this body of literature have not been replicated in community samples and may only apply to those with clinical levels of depression or substance abuse.

Permissive sexual values and attitudes have consistently been associated with infidelity. Not surprisingly, those who are more open to the idea of extradyadic relations are more likely to engage in such behaviors. Some research suggests that “personal readiness” to engage in infidelity is a salient predictor of being unfaithful.

If an individual has less sexual opportunity, it is more difficult for them to become extradya-dically involved. Individuals who have had more sexual opportunity in the past, such as those reporting a higher number of prior sexual partners, have been shown in some research to be more likely to engage in infidelity, although this is not a consistent finding.

Decisions to End an Affair

Although some cases of infidelity are one-time occurrences, others may be recurring and persist for many years. The decision to end an extradyadic relationship can be made by the individual having the affair, his or her primary partner, or by the extradyadic partner. A number of factors affect the decision to end an affair. Women with positive attitudes toward sex tend to carry on their extradyadic sexual relationships for longer periods. Men and women typically consider the rewards and costs of engaging in an extradyadic relationship: If the rewards of the relationship outweigh the costs of ending it, the relationship will persist until the opposite is true.

Emotional Responses to Infidelity

Infidelity evokes many emotions in both the betrayed partner and the partner that engaged in extradyadic activity, and many of these emotions, surprisingly, overlap. These may include symptoms of post-traumatic stress disorder, for example, disturbed sleep, irritability or anger outbursts, difficulty concentrating, hypervigilance, and recurrent intrusive thoughts about the affair. However, emotional responses may vary depending on the type of infidelity. Both women and men have been found to react to sexual infidelity with anger and blame but react to emotional infidelity with more hurt feelings. Where many studies have shown men and women to react similarly to a partner’s infidelity, some other research suggests women experience more emotional distress over all types of infidelity than men do.

Emotional responses to the initial disclosure of infidelity are usually intense. At the initial disclosure, powerful emotion is expressed through confrontation with the offending partner. However, some research shows a time lapse between the initial discovery and the expression of intense emotions. These emotions include, but are not limited to, insecurity, helplessness, abandonment, depression, and a desire for vengeance.

Once the intense emotional response passes, most individuals go through a time of making meaning of the event, evidenced by less emotional reactivity. This is often when crucial decisions about the future of the relationship are made.

Much research has focused on the jealous reactions men and women experience in response to various types of infidelity. Traditionally, among heterosexuals, men have been found to react with more jealousy when their partners have transgressed sexually, whereas women have been found to react with more jealousy to a partner’s emotional transgressions. Further, heterosexual men and women report less intense jealousy to a partner’s same-sex infidelity than to infidelity with an opposite-sex partner.

Research on jealousy in response to infidelity in same-sex couples has been mixed. In one study conducted in the mid-1990s, lesbian women reacted similarly to infidelity as their heterosexual counterparts, but gay men were found more often to react with distress to emotional infidelity than did heterosexual men. Study authors Michael Bailey and his colleagues suggested this is because homosexual men have a much higher tolerance for sexual jealousy than heterosexual men do, making emotional infidelity the more upsetting event. A second, more recent study, however, found lesbian women resembled heterosexual men (more jealous of sexual transgressions) and gay men resembled heterosexual women (more jealous of emotional transgressions). More research is needed to understand how jealousy resulting from different types of infidelity is manifested in same-sex relationships.

Relationship Outcomes

After an affair, the fate of the primary couple’s relationship depends on a number of factors. If the bond between the core couple is stronger than the bond between the extradyadic couple, it is more likely that the primary relationship will prevail. Also, the circumstance surrounding the extra-dyadic activity, for example who the extradyadic partner is and where the affair took place, can affect whether the primary relationship succeeds or fails. The extent to which the betrayed partner is willing to forgive the transgressor affects whether the primary relationship can continue and at what level it will function.

Jennifer Schneider found that 60 percent of the participants planned to leave their primary relationship once infidelity was disclosed, but less than 25 percent of those couples actually did so. Other research has found that in a large number of infidelity cases, the couple stays together but the relationship quality remains poor.

Infidelity spawns, and occurs in response to, a variety of relationship issues. If a couple is unable to work through these issues, or one individual is not open to rebuilding the trust in the relationship, the relationship may dissolve. Among married couples, infidelity independently predicts divorce. Men are more likely to end their relationship if their female partners were sexually unfaithful. Women, on the other hand, are more likely to end their relationship over emotional infidelity.

Some couples are able to keep their relationships intact after an extradyadic involvement. Research suggests that a subset of couples actually experience positive relationship outcomes after infidelity. These couples are often better able to communicate about the affair and work through their differences, either on their own or with the help of a therapist.

Therapeutic Implications

Infidelity often leads a couple to seek relationship counseling. Couples therapists report infidelity is one of the most difficult relationship problems to treat. Couples seeking therapy after an affair are often more distressed at the start of treatment than are couples in therapy for other issues. Therapists and clients have a number of important tasks to accomplish in therapy: gaining an understanding of why the affair occurred, expressing emotions, achieving forgiveness, and rebuilding trust. To reduce long-term resentment and hostility, it is critical that the betrayed spouse have the opportunity to express his or her feelings. Couples may also benefit from working on wider relationship issues, rather than focusing solely on the affair. There is limited research on the efficacy of couples therapy specific to couples who have experienced infidelity, and studies that have been conducted are based on small samples. Nonetheless, studies typically show improvement in couples functioning after broad-based couples counseling. Counselors working with couples on issues related to extradyadic sex must take the relationship context into account. Sex outside of a dyadic relationship is not, by nature, harmful if couples have agreed upon and feel comfortable with non-monogamy. This is most common among gay male couples, but does occur in heterosexual and lesbian couples as well. Therapists working with same-sex and opposite-sex couples will often use similar approaches; however, it is particularly important that practitioners consider unique cultural and relationship norms when evaluating the meaning and impact of the secondary sexual or emotional relationship.

Methodological Issues

Research on infidelity is plagued by a number of methodological issues that lead to inconsistencies in findings. Because of the taboo nature of extra-dyadic sexual behavior, social desirability is a serious obstacle to obtaining honest information related to incidence of infidelity. Mark Whisman and Douglas Snyder found that women were more likely to report being unfaithful when completing a computer-assisted survey than when directly interviewed by a researcher. As well, infidelity lacks a consistent operational definition, so comparing across studies can be difficult. Most research on infidelity is based on small, geographically limited samples of primarily Caucasian individuals. A large subset of this research is conducted on university student participants, who most often have not been married, posing a challenge to generalizability. Further, most researchers use cross-sectional designs. Because of this, it is difficult to discern whether relationship problems or other correlates of infidelity predated the transgression or occurred as a result. Finally, little is known about infidelity in cohabiting and lesbian couples. Future research is needed with samples that are more diverse in sexual orientation, marital status, socioeconomic status, and ethnicity.