Sexuality has biological, psychological, emotional, spiritual, social, and cultural aspects. It involves not only sexual behaviors but relationships, self-image, sex drive, reproduction, sexual orientation, and gender expression. Each person's sexuality is influenced by lifelong socialization, in which factors such as religious and cultural background play a part, and is expressed in self-esteem and the beliefs one holds about oneself (identifying as a woman, or as an attractive person). SCI is extremely disruptive to sexuality, and it most frequently happens to young people, who are at a peak in their sexual and reproductive lives. Yet the importance of sexuality as a part of life is not diminished by a disabling injury. Although for years people with SCI were believed to be asexual, research has shown sexuality to be a high priority for people with SCI and an important aspect of quality of life. In fact, of all abilities they would like to have return, most paraplegics rated sexual function as their top priority, and most tetraplegics rated it second, after hand and arm function. Sexual function has a profound impact on self-esteem and adjustment to life post-injury. People who are able to adapt to their changed bodies and to have satisfying sex lives have better overall quality of life. SCI usually causes sexual dysfunction, due to problems with sensation and the body's arousal responses. The ability to experience sexual pleasure and orgasm are among the top priorities for sexual rehabilitation among injured people. Much research has been done into erection. By two years post-injury, 80% of men recover at least partial erectile function, though many experience problems with the reliability and duration of their erections if they do not use interventions to enhance them. Studies have found that half or up to 65% of men with SCI have orgasms, although the experience may feel different than it did before the injury. Most men say it feels weaker, and takes longer and more stimulation to achieve. Common problems women experience post-SCI are pain with intercourse and difficulty achieving orgasm. Around half of women with SCI are able to reach orgasm, usually when their genitals are stimulated. Some women report the sensation of orgasm to be the same as before the injury, and others say the sensation is reduced. The severity of the injury is an important aspect in determining how much sexual function returns as a person recovers. According to the American Spinal Injury Association grading scale, an incomplete SCI is one in which some amount of sensation or motor function is preserved in the rectum.