Most young people in the United States begin having sexual intercourse during their teenage years. Current data suggest that slightly more than half of females and nearly two-thirds of males have had intercourse by their 18th birthday. In the last several decades there have been substantial increases in the proportion of adolescents who report sexual activity at each year of age. Increases have been greatest among females, especially among young females. Thus, more than twice as many females ages 14, 15, and 16 are sexually active now, compared with young women of the same ages just 15 years ago. Moreover, on average, there are seven years for women and ten years for men between first intercourse and first marriage. This creates a substantial interval of risk for non-marital pregnancy.
Initial sexual intercourse experiences are usually important (and sometimes defining) events in the lives of young people. Early timing of sexual initiation is important for two reasons. First, the younger the age of first sexual intercourse, the more likely that the experience was coercive, and forced sexual intercourse is related to long lasting negative effects. Secondly, the younger the age of first sexual intercourse, the greater the risk of unwanted pregnancy and sexually transmitted infections. This is because those who begin having sex at young ages are generally exposed to risk for a longer time, are less likely to use contraception, generally have more sexual partners, and tend to engage in higher risk sexual behaviors such as alcohol or drug use prior to sexual intercourse and having multiple concurrent sexual partners. It must be recognized as well that early intercourse is frequently not voluntary. Among females, as noted above, the majority of initial sexual experiences that occur at age 14 or younger are non-voluntary.
Many variables are related to the timing of first sexual intercourse. On average, males begin having sex at younger ages than females, and blacks begin at younger ages than whites or Hispanics. There are also strong effects of developmental characteristics, such as early puberty and high levels of androgen hormones (i.e., testosterone), which are associated with increased adolescent sexual behavior. Dating, and especially early steady dating, provides a context for many adolescent sexual experiences. Unconventional psychosocial attitudes and behaviors--as reflected by early use of alcohol, tobacco and other drugs, school problems, delinquency, and physical aggression--are associated with earlier onset of adolescent sexual intercourse. Parents' marital disruption and living with a single parent have been found to be associated with earlier onset of adolescent sexual behavior. This finding probably reflects a variety of factors, including lower family incomes, disadvantaged neighborhoods, lesser supervision, parental modeling, and more permissive attitudes in single parent families. Similarly, having sexually active siblings and friends is strongly related to a younger age at the onset of sexual activity. On the other hand, having better educated parents, supportive family relationships, parental supervision, sexually abstinent friends, good school grades and attending church frequently are all related to later onset of sexual intercourse.
In addition to families and schools, neighborhoods provide an environment within which adolescents make decisions related to sexual activity. The effects of the neighborhood environment, such as the community economic base and labor market conditions for women, account for a substantial portion of the racial differences among blacks and whites in the timing of first sexual intercourse. Thus, in one study, the overall risk of non-marital first intercourse was reported to be 50 percent higher for black teens than white teens, even controlling for individual and family level factors such as mothers' education and marital status and respondents' education and religious affiliation. The addition of contextual variables such as median family income, female unemployment, and female full-time employment reduced the racial difference in risk of first non-marital intercourse to 36 percent. Net of individual and family level factors, the only contextual variable found to be significant was female full-time employment in the community, which was related to a greater risk of first sex.