Some cultures find only sexual contact within marriage acceptable; however, extramarital sexual activity still takes place within such cultures. Unprotected sex poses a risk in unwanted pregnancy or sexually transmitted diseases. In some areas, sexual abuse of individuals is prohibited by law and considered against the norms of society.
As with other behaviors, human intelligence and complex societies have produced among the most complicated sexual behaviors of any animal. Most people experiment with a range of sexual activities during their lives, though they tend to engage in only a few of these regularly. Most people enjoy some sexual activities. However, most societies have defined some sexual activities as inappropriate (wrong person, wrong activity, wrong place, etc.) Some people enjoy many different sexual activities, while others avoid sexual activities altogether for religious or other reasons (see chastity, sexual abstinence). Some societies and religions view sex as appropriate only within marriage.
Some activities, known as sex crimes, are illegal in some jurisdictions, including those conducted between (or among) consenting and competent adults (examples include sodomy law and adult-adult incest). Scientific studies suggest sexual fantasy, even of unusual interests, is usually a healthy activity. Some people engage in various sexual activities as a business transaction. When this involves having sex with, or performing certain actual sexual acts for another person, it is called prostitution. Other aspects of the adult industry include (for example) telephone sex operators, strip clubs, pornography and the like.
Nearly all developed societies consider it a serious crime to force someone to engage in sexual behavior or to engage in sexual behavior with someone who does not consent. This is called sexual assault, and if sexual penetration occurs it is called rape, the most serious kind of sexual assault. The details of this distinction may vary among different legal jurisdictions. Also, precisely what constitutes effective consent to have sex varies from culture to culture and is frequently debated. Laws regulating the minimum age at which a person can consent to have sex (age of consent) are frequently the subject of political and moral debate , as is adolescent sexual behavior in general. Additionally, many societies have forced marriage, so consent does not really figure in to the equation of a sex crime.
These risks are raised by any condition (temporary or permanent) which impairs one's judgement, such as excess alcohol or drugs, or emotional states such as loneliness, depression or euphoria (e.g. new students at college). Carefully considered activity can greatly reduce all of these issues.
Due to health concerns arising from HIV/AIDS, chlamydia, syphilis, gonorrhea, HPV and other sexually transmitted infections, some people may want potential sex partners to be tested for STDs before engaging in sex.
Usually, though not always, such laws are termed sodomy laws, but also include issues such as age of consent laws, "decency" laws, and so forth. Laws prohibiting same-sex sexuality have varied widely throughout history, varying by culture, religious and social taboos and customs, etc. Often such laws are targeted or applied differently based on sex as well. For example, laws against same-sex sexual behavior in the United Kingdom during the reign of Queen Victoria, sodomy or "buggery" laws were aimed specifically at male same-sex sexual activity and did not target or even address female homosexuality. A well known example of such laws applied in relatively modern times can be found in the life story of Alan Turing.
Child sexual abuse is a form of child abuse in which a child is abused for the sexual gratification of someone else; child abuse is also a legal umbrella term describing criminal and civil offenses in which an adult engages in sexual activity with a minor or exploits a minor for the purpose of sexual gratification. In addition to direct sexual contact, child sexual abuse also occurs when an adult exposes their genitals to a child, asks or pressures a child to engage in sexual activities, displays pornography to a child, or uses a child to produce child pornography. The American Psychiatric Association states that "children cannot consent to sexual activity with adults", and condemns any such action: "An adult who engages in sexual activity with a child is performing a criminal and immoral act which never can be considered normal or socially acceptable behavior."
Effects of child sexual abuse include depression, post-traumatic stress disorder, anxiety, propensity to re-victimization in adulthood, and physical injury to the child, among other problems. Sexual abuse by a family member is a form of incest, and can result in more serious and long-term psychological trauma, especially in the case of parental incest.