Asexuality is distinct from abstention from sexual activity and from celibacy, which are behavioral; the latter is usually, but not always, for a religious reason. (For instance, sexual people in relationships with asexuals may become celibate as a result.) A sexual orientation, unlike a behavior, is definitionally "enduring". Some asexuals do have sex, despite lacking a desire for it.

In the mid-twentieth century, Alfred Kinsey rated individuals from 0 to 6 according to their sexual orientation from heterosexual to homosexual. He also included a category he called "X" for individuals with "no socio-sexual contacts or reactions". He labeled 1.5% of the adult male population as X. In Kinsey's second book, Sexual Behavior in the Human Female, he reported this breakdown of individuals who are X: unmarried females = 14–19%, married females = 1–3%, previously married females = 5–8%, unmarried males = 3–4%, married males = 0%, and previously married males = 1–2%.

Further empirical data about an asexual demographic appeared in 1994, when a research team in the United Kingdom carried out a comprehensive survey of 18,876 British residents, spurred by the need for sexual information in the wake of the AIDS pandemic. The survey included a question on sexual attraction, to which 1.05% of the respondents replied that they had "never felt sexually attracted to anyone at all." This study of this phenomenon was continued by the Canadian sexuality researcher Dr. Anthony Bogaert in 2004, who explored the asexual demographic in a series of studies. Bogaert believed that the 1% figure was not an accurate reflection of the likely much larger percentage of the population that could be identified as asexual, noting that in the initial survey 30% of people contacted chose not to participate in the survey. Since less sexually experienced people are more likely to refuse to participate in studies about sexuality, and asexuals tend to be less sexually experienced than non-asexuals, it is likely that asexuals were over-represented in the 30% who did not participate, compared to the 70% who did. The same study found the number of homosexuals and bisexuals combined to be about 1.1% of the population, which is much smaller than other studies indicate. However, Bogaert's sexuality research has been scrutinized in the past, since he was involved in studies that linked race to sexual behaviors as if they had an evolutionary basis. This study was highly debated by the scientific community as potentially constituting a case of scientific racism.

In a 1994 U.S. study that did not include asexuality as a sexual orientation, some people reported having had no sex or no partners in a year: 11.9% of adults, 9.8% of men, and 13.6% of women. In 5 years, the number of partners was zero for 8.0% of adults: 7.1% of men and 8.7% of women. In all of adulthood until the time of surveying (given that surveyed people were of different ages), the number of partners was zero for 2.9% of adults: 3.4% of men and 2.5% of women.

Asexuals, while typically lacking in sexual desire for either sex, may engage in purely emotional romantic relationships. Terms concerning this:

The Kinsey Institute sponsored another small survey on the topic in 2007, which found that self-identified asexuals "reported significantly less desire for sex with a partner, lower sexual arousability, and lower sexual excitation but did not differ consistently from non-asexuals in their sexual inhibition scores or their desire to masturbate".

A 1977 paper entitled Asexual and Autoerotic Women: Two Invisible Groups, by Myra T. Johnson, may be the first paper explicitly devoted to asexuality in humans. Johnson defines asexuals as those men and women "who, regardless of physical or emotional condition, actual sexual history, and marital status or ideological orientation, seem to prefer not to engage in sexual activity." She contrasts autoerotic women with asexual women: "The asexual woman [...] has no sexual desires at all [but] the autoerotic woman [...] recognizes such desires but prefers to satisfy them alone." Johnson's evidence is mostly letters to the editor found in women's magazines written by asexual/autoerotic women. She portrays them as invisible, "oppressed by a consensus that they are nonexistent," and left behind by both the sexual revolution and the feminist movement. Society either ignores or denies their existence or insists they must be ascetic for religious reasons, neurotic, or asexual for political reasons.

In a study published in 1979 in Advances in the Study of Affect, vol. 5, and in another article using the same data and published in 1980 in the Journal of Personality and Social Psychology, Michael D. Storms of the University of Kansas outlined his own reimagining of the Kinsey scale. Whereas Kinsey measured sexual orientation based on a combination of actual sexual behavior and fantasizing and eroticism, Storms only used fantasizing and eroticism. Storms, however, placed hetero-eroticism and homo-eroticism on separate axes rather than at two ends of a single scale; this allows for a distinction between bisexuality (exhibiting both hetero- and homo-eroticism in degrees comparable to hetero- or homosexuals, respectively) and asexuality (exhibiting a level of homo-eroticism comparable to a heterosexual and a level of hetero-eroticism comparable to a homosexual, namely, little to none). Storms conjectured that many researchers following Kinsey's model could be mis-categorizing asexual subjects as bisexual, because both were simply defined by a lack of preference for gender in sexual partners.

The first study that gave empirical data about asexuals was published in 1983 by Paula Nurius, concerning the relationship between sexual orientation and mental health. Unlike previous studies on the subject, she used the above-mentioned two-dimensional model for sexual orientation. Six hundred eighty-nine subjects—most of whom were students at various universities in the United States taking psychology or sociology classes—were given several surveys, including four clinical well-being scales and a survey asking how frequently they engaged in various sexual activities and how often they would like to engage in those activities. Based on the results, respondents were given a score ranging from 0 to 100 for hetero-eroticism and from 0 to 100 for homo-eroticism. Respondents who scored lower than 10 on both were labeled "asexual." This consisted of 5% of the males and 10% of the females. Results showed that asexuals were more likely to have low self-esteem and more likely to be depressed than members of other sexual orientations; 25.88% of heterosexuals, 26.54% bisexuals (called "ambisexuals"), 29.88% of homosexuals, and 33.57% of asexuals were reported to have problems with self-esteem. A similar trend existed for depression. Nurius did not believe that firm conclusions can be drawn from this for a variety of reasons. Asexuals also reported much lower frequency and desired frequency of a variety of sexual activities including having multiple partners, anal sexual activities, having sexual encounters in a variety of locations, and autoerotic activities.

Another study with both quantitative and qualitative sections has been done recently, but the results have not yet been published, though some of the results can be found online.