When you investigate infidelity, depression pops up surprisingly often. While I have written in other posts that infidelity has little to do with unhappiness in a relationship, there's quite a bit of evidence that extramarital sex does have some indirect links to feelings of sadness, unhappiness, and depression.
In most people, depression decreases libido and interest in sex. John Bancroft has proposed that there are some small numbers of people who experience an increase in sex drive when feeling the effects of depression. Poverty, and the emotional effects of it, affects men and women differently. When poverty goes up, and incomes go down, male infidelity increases, as female infidelity decreases. It may be that men use sex as an escape from the emotional burdens of poverty, but that poverty increases the risks and consequences that an unfaithful woman would incur, if caught cheating.
In the 1800's, Madame Germaine de Stael was a French political writer, a vocal opponent of Napoleon. She suffered severe depression throughout most of her life, and, it appears, used extramarital sex as a way to ward off the blues. In grief after the death of her first child, a daughter, Anna first pursued active and aggressive adultery, entering into sexual liaisons with several different men. Though not as beautiful as she may have wished to be, her sharp wit drew men to her like flies to honey. Seeking lovers to soothe her grief set something of a lifelong precedent for her. She wrote once to a lover, explaining that she had taken yet another lover, so that she might gain "a sort of excitement that would relieve for a moment the terrible weight that was pressing on my heart."
In Insatiable Wives, I interviewed several women and couples who discussed how their depression affected their pursuit of extramarital affairs. It wasn't that these women experienced an increase in sexual desire when depressed, but that they identified sex outside their marriage as one of the only ways they could change the ways they were feeling. In contrast to the existing theory, that depression was perhaps causing out-of-bounds sexual behavior (such as infidelity), the suggestion here is that this sexual behavior was actually adaptive, a means by which these women were manipulating their own body chemistry.
Assuming there is something here, what could be happening? I suggest there are perhaps at least three vehicles here, involved in extramarital affairs, which affect depression, at least in women: general biology, the specific neurochemistry of the brain, and psychology.
The psychological effects of extramarital sex can involve feelings of increased self-esteem, and feelings of attractiveness, that other men find a woman attractive. That attention, and the thrills of developing a new relationship, even the excitement and risk of cheating, can all reduce feelings of depression. Of course, the negative consequences of a discovered affair could certainly increase depression, but during the early stages of the affair, those symptoms might be reduced.
When women are having, or pursuing an affair, they take greater pains to appear attractive, take care of their bodies, and are healthier. They're having sex more, getting more exercise, and physiologically behaving in ways contrary to the lethargy and inactivity associated with most depression. And, in having more sex, they may be getting something else that fights depression: semen. Believe it or not, research by Gallup and Burch reveals that men have been using a secret chemical weapon in the sex war. When analyzed, men's semen is shown to contain high levels (higher than mere accident) of numerous psychoactive hormones and substances. These include testosterone (which increases a woman's libido and interest in having more sex), as well as neurochemicals. Epinephrine, norepinephrine, oxytocin, vasopressin, melatonin and other opioids are all present in semen, and all have detectable impact upon mood, cognition and memory. Gallup and Burch have shown that women who use condoms during sex have higher levels of depression. As the chemicals in semen are absorbed, vaginally, anally or orally, the woman experiences a real anti-depressant effect.
Neurochemically, a woman's brain reacts to a new sexual relationship with a tremendous flood of powerful substances that affect her mood and energy. Interestingly, serotonin levels drop, a condition also associated with depression. Serotonin is a chemical which helps us restrain impulses, and be more thoughtful and planning. Low levels of serotonin in new love contribute to our feelings of obsession and interest in our new partner. High levels of serotonin decrease libido and can even interfere in sexual arousal. This may be one reason it is so easy for a breakup in a passionate relationship to trigger a depressive episode, as the serotonin levels are already low. But, other powerful chemicals increase, taking the effects of serotonin into a positive, passionate direction. Oxytocin levels increase, which increase feelings of excitement and sensitivity to physical stimulation. Dopamine surges through the brain, acting as a chemical trigger for feelings of pleasure and reward in the brain. The woman's brain chemistry changes, and her mood along with it.
So, across many different physiological and psychological dimensions, a woman beginning a new relationship experiences an increase in feelings of pleasure, excitement, energy, and interest in life and her new lover.
Can I recommend that a depressed woman pursue an extramarital affair, to self-medicate her depressed brain, body and psyche? No, I can't say that. The social and relational impacts of infidelity and deception seem far too potentially devastating and risky, at least within most traditional marriages and relationships. But, are there women and men out there, engaging in extramarital sex when depressed, not as a result of the depression, but in an unconscious attempt to overcome those feelings, using one of the most powerful biological weapons in the human emotional arsenal? I strongly suspect this is likely, and that this may be an underlying dynamic that has not been addressed or considered in research or theory.