Libido (/lɪˈbiːdoʊ/; colloquial: sex drive) is a person's overall sexual drive or desire for sexual activity. Libido is influenced by biological, psychological, and social factors. Biologically, the sex hormones and associated neurotransmitters that act upon the nucleus accumbens (primarily testosterone and dopamine, respectively) regulate libido in humans.^[1] Social factors, such as work and family, and internal psychological factors, such as personality and stress, can affect libido. Libido can also be affected by medical conditions, medications, lifestyle and relationship issues, and age (e.g., puberty). A person who has extremely frequent or a suddenly increased sex drive may be experiencing hypersexuality, while the opposite condition is hyposexuality.

A person may have a desire for sex, but not have the opportunity to act on that desire, or may on personal, moral or religious reasons refrain from acting on the urge. Psychologically, a person's urge can be repressed or sublimated. On the other hand, a person can engage in sexual activity without an actual desire for it. Multiple factors affect human sex drive, including stress, illness, pregnancy, and others. A 2001 review found that, on average, men have a higher desire for sex than women.^[2]

Sexual desires are often an important factor in the formation and maintenance of intimate relationships in humans. A lack or loss of sexual desire can adversely affect relationships. Changes in the sexual desires of any partner in a sexual relationship, if sustained and unresolved, may cause problems in the relationship. The infidelity of a partner may be an indication that a partner's changing sexual desires can no longer be satisfied within the current relationship. Problems can arise from disparity of sexual desires between partners, or poor communication between partners of sexual needs and preferences.^[3]

Sigmund Freud, who is considered the originator of the modern use of the term,^[4] defined libido as "the energy, regarded as a quantitative magnitude... of those instincts which have to do with all that may be comprised under the word 'love'."^[5] It is the instinct energy or force, contained in what Freud called the id, the strictly unconscious structure of the psyche. He also explained that it is analogous to hunger, the will to power, and so on^[6]The%20New%20Wounded%3A%20From%20]]insisting that it is a fundamental instinct that is innate in all humans.^{[[7]](https://openlibrary.org/search?q=Klages%2C%20Mary%20%282017%29.%20} [[CITE|7|https://openlibrary.org/search?q=Klages%2C%20Mary%20%282017%29.%20*Literary%20Theory%3A%20The%20Complet)

Freud developed the idea of a series of developmental phases in which the libido fixates on different erogenous zones—first in the oral stage (exemplified by an infant's pleasure in nursing), then in the anal stage (exemplified by a toddler's pleasure in controlling his or her bowels), then in the phallic stage, through a latency stage in which the libido is dormant, to its reemergence at puberty in the genital stage.^[8][9]

Freud pointed out that these libidinal drives can conflict with the conventions of civilised behavior, represented in the psyche by the superego. It is this need to conform to society and control the libido that leads to tension and disturbance in the individual, prompting the use of ego defenses to dissipate the psychic energy of these unmet and mostly unconscious needs into other forms. Excessive use of ego defenses results in neurosis. A primary goal of psychoanalysis is to bring the drives of the id into consciousness, allowing them to be met directly and thus reducing the patient's reliance on ego defenses.^[10]

Freud viewed libido as passing through a series of developmental stages within the individual. Failure to adequately adapt to the demands of these different stages could result in libidinal energy becoming 'dammed up' or fixated in these stages, producing certain pathological character traits in adulthood. Thus the psychopathologized individual for Freud was an immature individual, and the goal of psychoanalysis was to bring these fixations to conscious awareness so that the libido energy would be freed up and available for conscious use in some sort of constructive sublimation.

According to Swiss psychiatrist Carl Gustav Jung, the libido is identified as the totality of psychic energy, not limited to sexual desire.^[11][12] As Jung states in "The Concept of Libido,"^[13] "[libido] denotes a desire or impulse which is unchecked by any kind of authority, moral or otherwise. Libido is appetite in its natural state. From the genetic point of view it is bodily needs like hunger, thirst, sleep, and sex, and emotional states or affects, which constitute the essence of libido." The Duality (opposition) creates the energy (or libido) of the psyche, which Jung asserts expresses itself only through symbols: "It is the energy that manifests itself in the life process and is perceived subjectively as striving and desire." (Ellenberger, 697) These symbols may manifest as "fantasy-images" in the process of psychoanalysis which embody the contents of the libido, otherwise lacking in any definite form.^[14] Desire, conceived generally as a psychic longing, movement, displacement and structuring, manifests itself in definable forms which are apprehended through analysis.

Defined more narrowly, libido also refers to an individual's urge to engage in sexual activity, and its antonym is the force of destruction termed mortido or destrudo.^[15]

Libido is governed primarily by activity in the mesolimbic dopamine pathway (ventral tegmental area and nucleus accumbens).^[1] Consequently, dopamine and related trace amines (primarily phenethylamine)^[16] that modulate dopamine neurotransmission play a critical role in regulating libido.^[1]

Other neurotransmitters, neuropeptides, and sex hormones that affect sex drive by modulating activity in or acting upon this pathway include:

A woman's desire for sex is correlated to her menstrual cycle, with many women experiencing a heightened sexual desire in the several days immediately before ovulation,^[31] which is her peak fertility period, which normally occurs two days before until two days after the ovulation.^[32] This cycle has been associated with changes in a woman's testosterone levels during the menstrual cycle. According to Gabrielle Lichterman, testosterone levels have a direct impact on a woman's interest in sex. According to her, testosterone levels rise gradually from about the 24th day of a woman's menstrual cycle until ovulation on about the 14th day of the next cycle, and during this period the woman's desire for sex increases consistently. The 13th day is generally the day with the highest testosterone levels. In the week following ovulation, the testosterone level is the lowest and as a result women will experience less interest in sex.^[17]

Also, during the week following ovulation, progesterone levels increase, resulting in a woman experiencing difficulty achieving orgasm. Although the last days of the menstrual cycle are marked by a constant testosterone level, women's libido may get a boost as a result of the thickening of the uterine lining which stimulates nerve endings and makes a woman feel aroused.^[33] Also, during these days, estrogen levels decline, resulting in a decrease of natural lubrication.

Although some specialists disagree with this theory, menopause is still considered by the majority a factor that can cause decreased sex desire in women. The levels of estrogen decrease at menopause and this usually causes a lower interest in sex and vaginal dryness which makes intercourse painful. However, the levels of testosterone increase at menopause and this may be why some women may experience a contrary effect of an increased libido.

Certain psychological or social factors can reduce the desire for sex.

These factors can include lack of privacy or intimacy, stress or fatigue, distraction or depression. Environmental stress, such as prolonged exposure to elevated sound levels or bright light, can also affect libido. Other causes include experience of sexual abuse, assault, trauma, or neglect, body image issues, and anxiety about engaging in sexual activity.^[34]

Physical factors that can affect libido include endocrine issues such as hypothyroidism, the effect of certain prescription medications (for example flutamide), and the attractiveness and biological fitness of one's partner, among various other lifestyle factors.^[35]

In males, the frequency of ejaculations affects the levels of serum testosterone, a hormone which promotes libido.

A study of 28 males aged 21–45 found that all but one of them had a peak (145.7% of baseline [117.8%–197.3%]) in serum testosterone on the 7th day of abstinence from ejaculation.^[36]

Anemia is a cause of lack of libido in women due to the loss of iron during the period.^[37]

Smoking, alcohol abuse, and the use of certain drugs can also lead to a decreased libido. Moreover, specialists suggest that several lifestyle changes such as exercising, quitting smoking, lowering consumption of alcohol or using prescription drugs may help increase one's sexual desire.

Some people purposefully attempt to decrease their libido through the usage of anaphrodisiacs.^[38] Aphrodisiacs, such as dopaminergic psychostimulants, are a class of drugs which can increase libido. On the other hand, a reduced libido is also often iatrogenic and can be caused by many medications, such as hormonal contraception, SSRIs and other antidepressants, antipsychotics, opioids and beta blockers.

Testosterone is one of the hormones controlling libido in human beings. Emerging research^[39] is showing that hormonal contraception methods like oral contraceptive pills (which rely on estrogen and progesterone together) are causing low libido in females by elevating levels of sex hormone binding globulin (SHBG). SHBG binds to sex hormones, including testosterone, rendering them unavailable. Research is showing that even after ending a hormonal contraceptive method, SHBG levels remain elevated and no reliable data exists to predict when this phenomenon will diminish.^[40]

Males reach the peak of their sex drive in their teens, while females reach it in their thirties.

(speculation) ^[41][42] The surge in testosterone hits the male at puberty resulting in a sudden and extreme sex drive which reaches its peak at age 15–16, then drops slowly over his lifetime. In contrast, a female's libido increases slowly during adolescence and peaks in her mid-thirties.^[43] Actual testosterone and estrogen levels that affect a person's sex drive vary considerably.

There is no widely accepted measure of what is a healthy level for sex desire.

Some people want to have sex every day, or more than once a day; others once a year or not at all.

However, a person who lacks a desire for sexual activity for some period of time may be experiencing a hypoactive sexual desire disorder or may be asexual. A sexual desire disorder is more common in women than in men. Erectile dysfunction may happen to the penis because of lack of sexual desire, but these two should not be confused.^[44] For example, large recreational doses of amphetamine or methamphetamine can simultaneously cause erectile dysfunction and significantly increase libido.^[45] However, men can also experience a decrease in their libido as they age.

The American Medical Association has estimated that several million US women suffer from a female sexual arousal disorder, though arousal is not at all synonymous with desire, so this finding is of limited relevance to the discussion of libido.^[37] Some specialists claim that women may experience low libido due to some hormonal abnormalities such as lack of luteinising hormone or androgenic hormones, although these theories are still controversial. Also, women commonly lack sexual desire in the period immediately after giving birth. Moreover, any condition affecting the genital area can make women reject the idea of having intercourse. It has been estimated that half of women experience different health problems in the area of the vagina and vulva, such as thinning, tightening, dryness or atrophy. Frustration may appear as a result of these issues and because many of them lead to painful sexual intercourse, many women prefer not having sex at all. Surgery or major health conditions such as arthritis, cancer, diabetes, high blood pressure, coronary artery disease or infertility may have the same effect in women.^[3] Surgery that affects the hormonal levels in women include oophorectomies.