Studies suggest around 30–40% of unmarried relationships and 18–20% of marriages see at least one incident of sexual infidelity.
Rates of infidelity among women are thought to increase with age.
It is more common for men compared to women to engage in extradyadic relationships.
The National Health and Social Life Survey found that 4% of married men, 16% of cohabiting men, and 37% of dating men engaged in acts of sexual infidelity compared to 1% of married women, 8% of cohabiting women, and 17% of women in dating relationships.
There is currently debate in the field of evolutionary psychology whether an innate, evolved sex difference exists between men and women in response to an act of infidelity; this is often called a "sex difference".
Those that posit a sex difference exists state that men are 60% more likely to be disturbed by an act of sexual infidelity (having one's partner engage in sexual relations with another), whereas women are 83% more likely to be disturbed by an act of emotional infidelity (having one's partner fall in love with another).
These differences have been generally thought due to evolutionary pressures that motivate men towards sexual opportunity and women towards commitment to one partner.
In addition, recent research finds that differences in gender may possibly be explained by other mechanisms including power and sensations seeking.
Depending on the context, men and women can experience social consequences if their act of infidelity becomes public.
The form and extent of these consequences are often dependent on the gender of the unfaithful person.
Correspondingly, monogamy and commitment are more commonplace.